UNIVERSITY   OF   CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL   EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


Studies  Preliminary  to  the  Establishment  of 

a  Series  of  Fertilizer  Trials  in  a 

Bearing  Citrus  Grove 

L.  D.  BATCHELOR,  E.  R.  PARKER,  and  ROBERT  McBRIDE 


BULLETIN  451 

APRIL,  1928 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1928 


STUDIES  PRELIMINARY  TO  THE  ESTABLISHMENT 
OF  A  SERIES  OF  FERTILIZER  TRIALS  IN  A 
BEARING  CITRUS  GROVE1 

L.  D.  BATCHELOE2  E.  R.  PARKER  3  and  ROBERT  McBBIDE* 


INTRODUCTION 

Many  fertilizer  and  cultural  trials  which  have  been  reported  upon 
have  been  conducted  under  the  implied  assumption  that  the  land  on 
which  the  trials  were  located  was  'uniform.'  However,  it  has  been 
evident  to  students  of  soil  fertility  during  the  last  two  decades,  that, 
in  reality,  the  productivity  of  the  soil  varies  greatly  in  different  sec- 
tions of  an  experimental  field.  In  some  instances  this  variability  of 
the  soil  has  masked  the  effect  of  fertilizer  trials  to  such  a  degree  that 
the  observed  results  have  been  very  misleading. 

Fertilizer  trials  conducted  on  land  which  has  not  been  subject  to 
previous  study  regarding  its  relative  productivity  for  the  crop  to  be 
experimented  with  must  ordinarily  be  considered  subject  to  large 
experimental  errors.  It  is  not  sufficient  to  test  the  variability  of  land 
with  one  crop  and  then  experiment  with  another.  This  point  has 
been  clearly  demonstrated  with  many  crops.  It  is  now  apparent  with 
oranges  on  the  Rubidoux  experimental  plots  of  the  Citrus  Experi- 
ment Station.  Here  such  soil  variations  have  been  created  by  twenty 
years  of  differential  fertilizer  trials  that  there  are  very  radical  differ- 
ences in  the  growth  and  production  of  orange  and  lemon  trees  on 
the  several  plots.  Clover  cover  crops,  however,  have  grown  almost 
equally  well  on  land  which  has  not  been  fertilized  for  twenty  years, 
and  on  plots  which  have  received  liberal  applications  of  'complete' 
fertilizer  for  the  same  period  of  time. 

The  present  study,  preliminary  to  the  establishment  of  a  rather 
large-scale  fertilizer  trial  in  a  bearing  orange  grove,  is  the  natural 


1  Paper  No.  178,  University  of  California,  Graduate  School  of  Tropical 
Agriculture  and  Citrus  Experiment  Station,  Riverside,  California. 

a  Professor  of  Orchard  Management  in  the  Citrus  Experiment  Station  and 
Graduate  School  of  Tropical  Agriculture,  and  Horticulturist  in  the  Experiment 
Station. 

a  Assistant  in     Orchard  Management,  Citrus  Experiment  Station. 
*  Assistant  Superintendent  of  Cultivations,  Citrus  Experiment  Station;  died 
February  1,  1927. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

outgrowth  of  the  attempt  to  profit  by  the  advances  which  have  been 
made  during  the  past  two  decades  in  the  methods  of  conducting  field 
trials.  Such  advances  have  resulted  from  the  studies  of  many  investi- 
gators both  in  this  country  and  abroad.  These  have  been  freely 
drawn  upon  as  a  guide  in  these  studies.  The  paper  here  presented  is 
principally  a  general  progress  report  in  the  nature  of  a  popular  dis- 
cussion. A  more  strictly  statistical  analysis  of  the  data  well  be  pre- 
pared for  publication  in  the  near  future. 

The  use  of  fertilizer  material  is  practically  a  universal  necessity 
of  citrus  culture  in  all  parts  of  the  world,  and  particularly  in  Cali- 
fornia. The  per-acre  charge  for  fertilizer  materials  in  this  state  will 
vary  from  a  few  dollars  to,  in  some  cases,  more  than  one  hundred 
dollars  a  year.  Any  study  which  will  give  additional  knowledge 
regarding  the  most  effective  and  economical  use  of  fertilizers,  and 
provide  a  means  by  which  the  effects  of  various  materials  upon  the 
soil  may  be  studied,  is  of  paramount  interest  to  those  engaged  in  the 
culture  of  citrus  fruit  in  California. 

Many  difficulties  are  encountered  in  obtaining  a  satisfactory 
orchard  to  be  used  for  a  complex  field  trial.  Commercial  orchards 
are  usually  much  too  variable  to  use  for  experimental  purposes.  They 
are  usually  located  upon  land  of  uncertain  history.  They  may  be 
growing  on  land  a  portion  of  which  has  receiver  a  fertilizer  treatment 
in  the  past  which  will  create  a  difference  in  productivity  of  the  soil, 
persistent  over  many  years.  The  trees  themselves  may  be  subject  to 
great  inherent  variability  of  size,  vigor,  and  productivity.  It  has 
been  demonstrated  by  several  investigators  that  the  rootstock  has  a 
great  effect  on  the  growth  of  the  trees,  at  least  during  their  early 
history.  Because  of  these  conditions  a  commercial  grove  may  be 
entirely  unsuited  to  experimental  use.  Other  observations  indicate 
that  variations  in  certain  characters  of  the  top  may  be  avoided  by 
careful  selection  of  bud  wood.  The  general  planting  plan,  also,  of  an 
experimental  orchard  may  vary  from  that  ordinarily  employed  in  a 
commercial  planting.  Careful  planning  of  an  experimental  planting 
may  decrease  the  effort  required  in  maintaining  it,  as  compared  with 
a  commercial  orchard  adapted  to  the  purpose.  It  also  may  facilitate 
the  reduction  of  the  experimental  error  by  making  possible  the  appli- 
cation of  recognized  methods  of  plot-trial  technic. 

The  final  value  of  the  use  of  different  fertilizer  materials  may  not 
be  fully  established  until  they  have  been  applied  to  the  same  plots  for 
many  years.  The  trials  herein  discussed  may  therefore  be  expected  to 
continue  for  a  period  of  twenty  or  thirty  years.     In  consideration  of 


BuL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  5 

all  of  these  facts  it  is  desirable  to  carry  on  such  trials  upon  publicly 
owned  property.  In  this  case  change  in  ownership  will  not  necessi- 
tate the  modification  or  discontinuation  of  experiments  which  may,  if 
continued,  be  productive  of  additional  useful  information. 

In  view  of  the  foregoing  comments  it  appeared  necessary  in  1914 
that  an  orchard  be  established  for  the  specific  purpose  of  using  it  for 
fertilizer  trials.  The  orchard  described  herein  was  planned  in  an 
effort  to  make  it  as  satisfactory  as  possible  for  this  use. 


HISTORY  OF   LAND   AND    ESTABLISHMENT  OF   THE   GROVE, 
INCLUDING   PROPAGATION   AND   CULTURE 

GENEEAL  HISTORY  AND  DESCRIPTION  OF  THE  LAND 

The  establishment  of  the  fertilizer  trials  herein  discussed  was  one 
of  the  recognized  objectives  of  the  Citrus  Experiment  Station  when 
a  new  site  was  purchased  in  the  year  1914.  The  land  chosen  for 
planting  the  experimental  grove  was  selected  largely  because  of  the 
apparent  uniformity  of  the  soil,  and  of  the  past  cultural  practices. 
Thus  it  was  deemed  particularly  suitable  for  the  purpose  of  conduct- 
ing the  trials  under  consideration.  It  seems  desirable  at  this  time  to 
discuss  somewhat  in  detail  the  history  and  the  cultural  treatment  of 
the  land  during  the  periods  preceding  and  following  the  planting  of 
the  trees,  and  especially  during  the  latter  period. 

The  soil  is  classified  as  Ramona  loam  by  the  United  States  Depart- 
ment of  Agriculture  soil  survey.5 

The  land  was  first  cleared  in  1875  and  planted  to  grain  in  1876. 
From  this  date  until  the  purchase  of  the  land  by  the  state  in  1914  it 
was  sown  annually  to  barley  or  wheat,  with  the  exception  of  an 
occasional  year  during  which  the  soil  was  left  fallow. 

The  land  slopes  gradually  toward  the  west,  with  an  average  grade 
of  1%  per  cent.  No  systematic  effort  to  grade  or  level  the  land  was 
made  during  the  time  it  was  cropped  to  grain,  so  far  as  is  known. 
The  ordinary  plowing  and  harrowing,  however,  would  fill  in  the  small 
depressions  which  normally  occur  in  newly  cleared  land,  and  doubt- 
less the  land  presented  a  much  smoother  general  aspect  at  the  time  of 


s  The  soil  is  of  old  alluvial  origin.  It  is  derived  from  granite  rock,  and 
contains  some  mica.  The  soil  to  a  depth  of  about  12  inches  consists  of  a  rather 
friable,  light-textured,  gritty  loam  of  brown  color.  It  is  very  slightly  reddish 
brown  when  wet.  The  substratum  is  a  compact  gritty  loam  of  greatly  varying 
thickness;  occasionally  it  extends  to  a  depth  of  only  4  feet  from  the  surface, 
but  rarely  extends  to  20  feet  from  the  surface.  Below  this  formation  the 
lower  strata  become  gradually  so  compact  that  they  can  be  penetrated  only 
with  great  difficulty. 


b  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

purchase  in  1914,  after  thirty-eight  years  of  dry  farming,  than  it 
did  when  the  brush  was  first  cleared  from  the  land  in  1875.  This 
natural  filling  in  of  depressions  and  the  lowering  of  the  higher  local 
areas  of  soil,  which  would  unavoidably  occur  during  nearly  four 
decades  of  farming,  may  in  a  measure  account  for  some  of  the  marked 
differences  in  productivity  between  small  adjacent  areas,  which  will 
be  more  fully  discussed  later. 

The  surface  was  sufficiently  smooth  in  1914  so  that  only  a  very 
slight  amount  of  grading  of  the  surface  soil  was  necessary  in  prepar- 
ing the  land  for  irrigation.  This  grading  was  done  only  on  the  west 
edge  of  the  field.  The  irrigation  system  was  installed  during  the 
spring  of  1917  and  the  land  was  irrigated  for  the  first  time  during 
May  and  June  of  that  year. 

Figure  1  shows  the  shape  of  the  field  and  the  arrangement  of  the 
experimental  plots. 

THE  PEOPAGATION  OF  THE  TREES 

Selection  in  the  Nursery. — It  was  recognized  in  planning  the 
experiment  that  one  of  the  requisites  for  the  accuracy  of  the  future 
experiments  was  to  secure  uncommonly  uniform  nursery  trees.  This 
is  essential  in  order  that  the  trees  in  all  future  plots  will  be  as  nearly 
equal  as  possible  in  size  and  yielding  capacity.  Extra  care,  beyond 
that  used  in  the  ordinary  commercial  production  of  trees,  has  been 
exercised  to  effect  a  reduction  of  differences  between  trees.  Varia- 
tions which  might  be  inherent  either  in  the  rootstocks  used  or  in  the 
parent  trees  from  which  buds  were  taken  have  both  been  considered  in 
the  nursery. 

The  following  measures  were  followed  to  produced  especially 
uniform  trees : 

1.  The  sweet  orange  (Citrus  sinensis)  nursery  stock  which  was 
transplanted  from  the  seed  bed  to  the  nursery  in  1914,  was  thoroughly 
culled  and  the  undersized  trees  were  discarded.  These  discards 
amounted  to  possibly  15  per  cent  of  the  seedlings. 

2.  After  one  year's  growth  in  the  nursery,  and  at  the  time  the 
1  rees  were  budded  in  1915,  another  selection  of  the  small-sized  trees 
was  made,  and  these  were  discarded. 

:>.  When  the  trees  were  dug  from  the  nursery  for  transplanting 
to  the  grove  in  1917,  the  small-sized  budded  trees  were  culled  from 
the  lot,  making  a  third  discarding  of  trees  which  lacked  vigor  and 
size.  Thus  from  the  establishment  of  the  nursery  until  the  actual 
planting  of  the  grove,  an  endeavor  was  continuously  made  to  produce 
a  vigorous  and  unusually  uniform  lot  of  trees. 


BuL.  451 J  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  7 


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Fig.  1. — Plan  of  experimental  field,  showing  arrangement   of 
blocks  and  plots. 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Selection  of  Buds — Plump,  well-formed  buds  from  mature  bud 
wood  were  used  for  propagation  purposes.  Only  such  twigs  were 
used  as  showed  blossoms  formed  or  in  process  of  formation  on  the 
tips  of  the  current  season's  growth  at  the  time  the  bud  wood  was 
cut.  The  Washington  Navel  orange  trees  that  are  to  form  the  experi- 
mental rows  were  propagated  from  trees  for  which  yield  records  had 
been  kept  for  several  years.  Only  the  heavy-producing  trees  were 
used  as  a  source  of  bud  wood. 

The  grapefruit  trees  were  propagated  from  high-yielding  parent 
trees  of  recorded  performance.  The  Valencia  bud  wood,  on  the 
other  hand,  came  from  trees  which  were  true  to  type,  but  not  from 
performance-record  trees. 

PEEPAEING  THE  LAND 

The  actual  preparation  of  the  land  for  tree  planting  began  during 
the  fall  and  early  winter  of  1915.  The  land  was  deeply  plowed  at 
that  time;  part  of  the  area  was  dry-plowed  with  a  disk  plow  in  the 
fall  and  the  remainder  was  plowed  with  a  moldboard  plow  after  the 
rainy  season  began.  The  main  portion  of  the  field,  that  west  of  the 
canal  lay  in  a  rough  fallow  condition  until  the  summer  of  1916,  when 
it  was  again  plowed.  This  latter  plowing  was  not  deep  and  was  done 
primarily  to  kill  the  weed  growth. 

.  The  small  portion  of  the  field  east  of  the  canal  (12.7  acres),  as 
shown  by  figure  1,  was  not  prepared  exactly  as  heretofore  noted  for 
the  main  portion  of  the  field.  A  crop  of  oat  hay  was  produced  on 
this  area  during  the  spring  of  1916.  The  land  was  then  left  in  grain 
stubble  until  tree  planting  began  in  the  spring  of  1917. 

PLANTING  THE   TEEES 

During  the  spring  of  1917,  a  narrow  strip  of  land  was  plowed 
where  each  future  tree  row  was  to  be  located.  The  tree  holes,  24 
inches  deep  and  24  inches  in  diameter,  were  dug  early  in  May.  A  pre- 
liminary soil  survey  was  made  by  making  a  hole  4  feet  deep  from  the 
surface  of  the  ground  with  a  soil  tube,  in  each  hole  which  was  dug 
for  tree  planting.  Slightly  less  than  10  per  cent  of  the  holes,  that 
showed  a  semi-impervious  layer  within  4  feet  of  the  surface  of  the 
ground  were  blasted.  Before  the  actual  planting  began,  the  surface 
soil  was  filled  back  into  the  holes  to  a  depth  of  12  inches  from  the 
surface.  The  soil  was  then  settled  by  irrigating  the  rows  of  holes 
before  planting  the  trees.  After  the  trees  were  planted,  they  were 
thoroughly  irrigated  to  settle  the  soil  around  the  roots. 


5     7. 


BUL.  451]  FERTILIZER    TRIALS   IN    A    BEARING    CITRUS    GROVE  9 

The  entire  orchard  was  planted  in  pairs  of  blocks  each  ten  trees 
deep.  Separate  irrigation  lines  were  ultimately  laid  for  each  of  these 
blocks,  so  that  each  block  of  trees  may  be  irrigated  separately.  The 
Washington  Navel  orange  trees  were  planted  as  the  test  variety.  Each 
alternate  row  constitutes  an  experimental  plot  and  contains  eight 
trees  of  this  variety.     The  first  tree  of  each  test  row,  next  to  the  pipe 

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Fig.  2. — Showing  arrangement  of  trees  in  plots  and  guard  rows. 

line,  however,  is  a  Valencia  orange  tree  and  the  tenth  tree  is  a  grape- 
fruit tree.  The  rows  alternating  with  the  test  rows  are  planted 
throughout  the  orchard  to  Valencia  and  grapefruit  trees  alternating. 
These  latter  rows  will  be  considered  guard  rows  between  the  fertilizer 
plots  and  are  designed  to  prevent  to  some  extent  the  overlapping  of 
the  effects  of  different  fertilizer  treatments  from  one  Navel  roAV  to 
another.  The  plan  of  planting  may  be  more  clearly  understood  by 
reference  to  figure  2,  which  shows  portions  of  two  blocks  of  the 
experimental  field. 


rc&  BLOC*   £ 


10  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


INTERCROPPING    THE    GROVE    DURING    THE    SUMMER    SEASONS    OF 
THE  FIRST  FOUR  YEARS 

The  land  between  the  tree  rows  remained  in  a  fallow  condition 
during'  the  planting  operations.  As  soon  as  the  trees  were  set,  this 
space  was  prepared  for  planting  beans,  The  beans  were  planted  in 
rows  36  inches  apart  with  six  rows  of  beans  in  each  interspace  between 
the  orange  tree  rows. 

During  the  first  four  years  of  the  existence  of  the  grove  it  was 
inter-cropped  each  summer  to  Blackeye  beans  (Vigna  sinensis)  and 
planted  to  a  bitter  clover  (Melilotus  indica)  cover  crop  each  fall. 
The  winter  cover  crop  was  planted  in  September  and  plowed  under 
during  the  following  February  or  March.  Figure  3  shows  a  view  of 
a  portion  of  the  experimental  field  during  the  first  year,  before  the 
harvest  of  the  bean  crop. 

The  yearly  intercropping  of  the  land  to  Blackeye  beans  for  four 
years  furnished  considerable  straw  to  apply  as  a  fertilizer  material 
to  the  young  trees.  This  bean  straw  was  applied  in  deep  furrows. 
The  first  year  a  furrow  was  made  with  a  large  moldboard  plow  on 
each  side  of  the  tree  rows  at  a  distance  of  2%  feet  from  the  trees. 
The  bean  straw  was  buried  in  the  furrows  on  two  sides  of  the  trees, 
distributed  along  a  space  of  3  or  4  feet  in  the  furrow.  An  average 
of  20  pounds  of  bean  straw  per  tree  was  applied. 

During  the  fall  of  the  second  year  (1918)  all  the  bean  straw  pro- 
duced as  an  inter-crop  and  also  about  ten  tons  produced  on  nearby 
fields,  was  applied  in  furrows  to  the  48  acres  of  the  experimental 
field.  The  furrows  were  made  parallel  to  the  tree  rows,  placed  about 
one  foot  further  away  from  the  trees  than  the  furrows  of  the  1917 
season.  In  addition  to  this,  one  furrow  on  each  side  of  the  trees  was 
made  across  the  tree  rows,  at  a  distance  of  4  feet  from  the  tree  trunk. 
All  the  furrows  were  made  about  12  inches  deep.  The  straw  was 
applied  at  the  rate  of  24  pounds  per  tree.  Figure  4  shows  the  method 
of  applying  the  straw  along  the  tree  rows  during  the  second  year. 
It  was  trampeled  down,  and  then  covered  over  by  using  a  moldboard 
plow.  An  examination  of  this  straw  in  January,  1919,  showed  that 
the  straw  was  covered  with  an  average  of  5  inches  of  soil. 

During  the  early  fall  of  1919  furrows  were  again  made  parallel 
to  the  tree  rows  one  foot  further  away  from  the  rows  than  the  pre- 
vious year,  making  a  total  of  4^  feet  and  straw  was  applied  at  the 
rate  of  17  pounds  per  tree. 


BuL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


11 


Fig.  3. — View  of  part  of  the  experimental  orchard,  looking  in  southwestern 
direction,  during  the  first  year  (1917).  The  summer  inter-crop  between  the  tree 
rows  may  be  seen. 


Fig.  4. — Method  of  applying  bean  straw  in  furrows  during 
second  year  (1918). 


12 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  orchard  was  intercropped  to  Blackeye  beans  during  the  sum- 
mer of  1920  for  the  last  time.  After  the  bean  harvest  of  that  year 
the  straw  was  applied  in  furrows  made  across  the  tree  rows  and  so 
placed  that  they  were  about  one  foot  from  the  cross  furrows  made  in 
1918  and  thus  approximately  5  feet  from  the  tree  trunks.  Ten  pounds 
of  straw  was  applied  per  tree ;  only  75  per  cent  of  this  straw  had  been 
produced  as  an  intercrop,  the  remainder  having  been  grown  on 
nearby  land. 


>^>;  w  * 


Fig.  5\ — Summer  cover  crop  of  Whippoorwill  cowpeas,  1921. 


CULTURE  OF  THE  GROVE  DURING  SUMMER  SEASONS  OF  FIFTH  TO 
NINTH  YEARS,  INCLUSIVE 

In  both  1921  and  1922,  summer  cover  crops  of  Whippoorwill  cow- 
peas  (Vigna  sinensis)  were  grown.  The  cowpeas  were  planted  in 
lows  and  cultivated  during  the  interval  between  irrigations  until  the 
growth  of  their  tops  made  this  operation  no  longer  practicable.  They 
were  planted  in  May  and  disked  under  about  the  middle  of  August 
with  a  double  disk  and  tractor  power.  A  relatively  heavy  production 
was  secured  each  year.  The  green  weight  of  the  crop  for  1921  was 
10.5  tons  to  a  solid  acre  of  cowpeas,  and  for  1922  it  was  13.8  tons. 
Although  the  cowpeas  were  planted  in  the  tree  rows  in  1921,  the  irri- 
gation water  did  not  reach  them  well  and  the  crop  there  was  stunted. 


BUL.  451J  FERTILIZER    TRIALS    IN    A    HEARING    CITRUS    GROVE  13 

For  this  reason  only  three-quarters  of  the  land  was  really  productive 
of  a  cover  crop  that  year.  During  the  1922  season,  however,  per- 
manent irrigation  furrows  were  made  in  the  form  of  a  figure  eight 
between  each  two  trees  in  the  tree  rows.  This  method  of  irrigation 
produced  as  good  tonnage  of  cowpeas  in  the  tree  rows  as  in  the  inter- 
spaces, and  all  the  land  except  that  actually  under  the  trees  produced 
a  summer  cover  crop.  The  appearance  of  the  grove  and  the  summer 
cover  crop  in  1921  is  well  illustrated  by  figure  5. 

WINTEE   COVER-CROPPING 

Throughout  the  entire  history  of  the  grove  with  the  exception  of 
1926-27,  a  cover  crop  has  been  grown  during  the  winter  seasons. 
Yellow  bitter  clover  (M.  inclica)  has  been  used  every  year  except 
1923-24  when  purple  vetch  (V.  at ro purpurea)  was  used.  A  good 
commercial  tonnage  of  winter  cover  crop  has  been  grown  six  years 
out  of  nine.  During  the  spring  of  1922  and  also  of  1923  the  tonnage 
plowed  under  was  very  light,  owing  to  the  destruction  during  the 
previous  fall  months  of  many  of  the  young  clover  plants  by  the  alfalfa 
caterpillar  (Eurymus  eurytheme) .  The  crop  of  purple  vetch  plowed 
under  in  1924  was  also  relatively  light  because  of  the  ravages  of  the 
destructive  pea  aphis  (Macrosiplium  pisi),  which  greatly  reduced  the 
growth  of  the  crop  the  last  two  weeks  before  it  was  plowed  under. 
The  average  annual  jdeld  was  about  11  tons  of  green  weight  to  a 
solid  acre  of  cover  crop.  The  approximate  average  green  weight  per 
acre  was  13  tons  in  1925  and  11  tons  in  1926. 

During  the  years  when  Blaekeye  beans  were  grown  as  an  inter- 
crop, the  winter  cover  crop  was  sown  as  early  as  possible  after  the 
bean  harvest,  which  was  usually  the  latter  part  of  September  or 
early  October.  It  was  then  plowed  under  by  the  middle  of  March. 
This  gave  plenty  of  time  for  the  green  material  to  decompose  and 
the  land  to  be  prepared  for  bean  planting.  Since  the  fall  of  1921  the 
winter  cover  crop  has  been  planted  earlier  than  heretofore,  usually 
about  the  last  week  in  August  or  the  first  week  in  September.  The 
crops  have  been  plowed  under  during  the  last  ten  days  in  February 
for  the  last  five  years.  Throughout  the  whole  life  of  the  grove  the 
winter  cover  crop  has  been  plowed  under  to  a  depth  of  from  9  to  10 
inches  with  a  moldboard  plow  and  tractor  power. 

During  the  summer  seasons  of  1923  to  1926,  inclusive,  clean  cul- 
ture was  practiced.  The  first  two  years  of  this  period  the  soil  was 
worked  two  or  three  times  during  the  time  intervening  between  two 
irrigations.     The  usual  practice  was  to  harrow  over  the  grove  with  a 


14  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

spike-tooth  harrow  as  soon  as  the  land  was  sufficiently  dried  out  after 
an  irrigation.  It  was  then  cultivated  both  with  the  tree  rows  and 
crosswise,  with  a  heavy  cultivator  drawn  by  a  tractor.  This  program 
of  cultivation  for  the  summer  months  was  judged  to  be  excessive,  and 
was  modified  beginning  with  the  summer  of  1925.  During  the  last 
three  summers  the  irrigation  furrows  have  been  allowed  to  become 
thoroughly  dry  without  being  '  pulled  in '  by  the  use  of  a  harrow.  The 
land  has  been  merely  cultivated,  ordinarily  only  one  way,  with  a 
heavy  cultivator,  between  irrigations.  The  land  has  been  thoroughly 
dry,  so  that  some  clods  have  been  formed  by  the  cultivation.  The 
furrows  for  the  next  irrigation  have  been  made  approximately  one 
week  after  cultivation  and  have  been  allowed  to  remain  open  for  a 
week  or  ten  days  before  irrigation.  The  modification  of  the  cultural 
practice  by  reducing  the  number  of  cultivations  between  irrigations 
has  been  followed  by  a  marked  improvement  in  the  readiness  with 
which  the  soil  has  absorbed  irrigation  water. 


IREIGATION  PRACTICE 

The  irrigation  practice  followed  has  been  in  general  similar  to 
that  employed  under  commercial  management  of  like  properties  of  the 
district.  The  nature  of  the  soil  and  the  slope  of  the  land  has  made 
it  advisable  to  use  the  furrow  method  of  irrigation  exclusively.  From 
2%  to  4  acre  inches  of  water  per  acre  has  been  the  usual  single  appli- 
cation. During  the  years  when  intercrops  or  summer  cover-crops 
were  grown  between  the  tree  rows  the  land  was  irrigated  in  accord- 
ance with  the  demands  of  the  annual  crop,  with  the  exception  that  one 
furrow  on  each  side  of  the  young  trees  was  used  to  give  them  water 
at  frequent  intervals,  regardless  of  the  needs  of  the  intercrop. 

The  time  of  irrigation  of  the  grove  and  cover  crops  has  always 
been  determined  by  the  moisture  content  of  the  soil.  This  has  ordi- 
narily been  accomplished  by  the  frequent  use  of  a  soil  tube  in  various 
parts  of  the  field.  In  addition,  beginning  with  the  year  1922,  a  record 
has  been  kept  of  the  moisture  content  of  the  soil,  in  plots  distributed 
at  random  throughout  the  field.  When  only  the  needs  of  the  trees 
have  been  considered  the  average  interval  between  irrigations  during 
the  summer  months  has  been  from  twenty-five  to  thirty  days. 

The  winter  cover  crops  have  been  irrigated  at  frequent  intervals 
during  the  fall  months.  The  usual  absence  of  rains  during  the  period 
From  September  to  November,  inclusive,  has  made  it  advisable  during 
most  years  to  apply  a  light  irrigation  every  fourteen  to  twenty-one 


Buu451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


15 


days  in  order  to  keep  up  a  continuous  growth  of  the  young  cover- 
crop  plants.  The  total  amount  of  water  applied  annually  has  varied 
from  30  to  48  acre  inches  per  acre,  according  to  the  rainfall  and  the 
needs  of  the  intercrops. 

One  notable  objection  to  the  growing  of  a  summer  cover  crop  of 
cowpeas  has  been  the  lack  of  penetration  of  the  irrigation  water,  when 
it  is  necessary  to  run  water  time  after  time  in  the  same  irrigation 
furrows.     During  the  latter  part  of  the  growth  of  the  cover  crop, 


225 


cvix#<oa>ocvj^;vaa>oc\j.^ir>c9oc\j^voa>ot\i     <* 

•HrHiHr-lrHCVlCMCMCM  tOtOtOnW^-J3 


FLOT  NUMBERS 

Fig.  6. — Average  yield  per  tree  in  each  plot  of  Block  I,  for  each  of  six 
years,  1922  to   1927,  inclusive. 


from  July  15  to  August  15,  it  has  been  practically  impossible  to  wet 
the  soil  below  2  feet  from  the  surface.  This  system  of  culture  may 
be  seriously  objected  to  on  the  Ramona  loam  soil,  and  similar  soil 
types,  because  of  the  lack  of  penetration  of  the  irrigation  water. 
The  maximum  demand  of  the  intercrop  for  water  comes  at  a  time 
when  the  midsummer  demand  of  the  fruit-laden  trees  is  also  high.  It 
has  been  literally  impossible  to  apply  sufficient  water  for  both  crops 
on  the  soil  types  here  encountered.  Allowing  the  water  to  run  24 
hours  per  irrigation  it  was  impossible  to  apply  more  than  0.8  to  1.0 
acre  inch  per  acre.     With  a  48-hour  run  usually  less  than  2.0  acre 


16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


inches  per  acre  could  be  applied.  Running  water  continuously  for 
48  to  72  hours  did  not  accomplish  a  satisfactory  irrigation.  Under 
such  conditions  it  has  been  necessary  to  apply  water  every  seven  to 
ten  days  and  even  then  the  very  small  amount  taken  up  by  the  soil 
was  insufficient  for  the  best  development  of  the  young  trees. 

The  results  of  the  two  years  of  summer  cropping  to  Whippoorwill 
cowpeas  in  this  orchard  have  shown  clearly  that  practically  no  sum- 
mer growth  of  the  trees  took  place  from  June  to  August,  inclusive. 


JlllIIBBB 

-  =  =p:  — 5^S;  s; 1    "zh^-h^^U   1    ^j^T "l   klc^3J~~SlN_i'  [ — h"" — 

\--& ^S 5 »BS;- "IS 2 & j-f- "^t2--   ,  "t"S^-_L  — L-  r>4j  | 

(tV                 ***i              ~""r"~"    ■'                              """M^i       '  i 

Ny                          /        '                                                                      S>»                    ....                                                                                           """^S*"^             i 

==^=::-V ^,1926 _ lisSlIIi: 

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70 ^_*5*_ 5*.„^ TH^T  z~~ 

s— V 1— 1 1 1 

:Eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee|ee_ee|eeeeeee|eee 

>EFGHIJKLM 
BLOCKS 

-Average  yield  per  tree  in  each  block,  for  each  of  six  years, 
1922  to  1927,  inclusive. 


A  month  after  the  cover  crop  was  disked  under,  or  about  September 
15,  growth  started  on  the  trees  and  became  exceedingly  great  by 
October  15  to  November  1.  The  frost  hazard  naturally  became  much 
greater  under  such  conditions  than  when  the  trees  made  three  or  four 
normal  cycles  of  growth  during  the  growing  season  and  entered  the 
autumn  period  in  a  well-matured  condition. 

The  practices  which  have  been  pursued  in  the  development  and 
culture  of  this  orchard  have  resulted  in  the  production  of  a  very 
satisfactory  property  from  a  commercial  viewpoint.     The  size  and 


BuL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


17 


productivity  which  the  trees  have  attained,  especially  during  the  first 
six-year  period,  have  been  somewhat  greater  than  that  usually  reached 
during  the  same  interval  of  time  on  similar  properties. 


TABLE  1 

Average  YrELD  Per  Tree  in  each  Plot  of  Block  I,  for  each  of  Six  Years, 

1922  to  1927,  Inclusive 


Plot 


Year 


lfi 


20 


22 


24 


2li 


28 


30 


32 


34 


36 


38 


40 


42 


Average  yield  per  tree,  in  po 

unds 

1922 

90 

112 

123 

104 

91 

85 

75 

83 

87 

85 

105 

82 

93 

88 

114 

78 

68 

117 

87 

90 

93 

83 

1923 

63 

62 

79 

68 

55 

55 

51 

75 

60 

68 

86 

86 

64 

75 

103 

81 

69 

104 

88 

82 

86 

58 

1924 

149 

145 

162 

171 

146 

151 

143 

153 

156 

165 

183 

158 

147 

172 

196 

162 

142 

186 

172 

175 

177 

153 

1925 

145 

151 

171 

164 

145 

141 

131 

123 

135 

135 

153 

116 

116 

149 

155 

140 

134 

158 

152 

171 

157 

140 

1926 

103 

106 

119 

107 

126 

113 

101 

106 

116 

127 

136 

93 

95 

117 

151 

117 

128 

132 

141 

144 

146 

139 

1927 

128 

144 

183 

157 

168 

132 

146 

140 

164 

167 

163 

154 

186 

172 

193 

178 

187 

203 

177 

187 

204 

181 

Avg. 

113 

120 

140 

129 

122 

113 

108 

113 

120 

125 

138 

115 

117 

129 

152 

126 

121 

150 

136 

142 

144 

126 

It  is  believed  that  the  practice  of  growing  leguminous  intercrops 
has  been  of  distinct  advantage  in  improving  and  maintaining  the 
yields  of  this  orchard.  The  appearance  of  the  trees  and  the  yields 
now  indicate,  however,  that  the  growing  of  winter  cover  crops  as 
practiced  and  without  the  use  of  fertilizer  material  is  not  maintaining 
the  trees  in  a  condition  of  greatest  vigor.  As  indicated  in  figures 
6  and  7  and  also  in  table  1,  the  yields  of  the  trees  have  not  been 
increased  since  1924  until  the  year  1927.  Although  the  latter  was 
an  exceptionally  good  year  for  orange  production  in  this  district, 
only  a  slight  increase  over  the  yield  of  1924  was  recorded.  The 
present  appearance  of  the  trees  also  shows  that  they  are  not  in  a 
condition  of  luxuriant  growth.  In  comparison  with  well-fertilized 
orchards  in  the  vicinity,  the  new  growth  appearing  on  the  Navel 
orange  trees  during  the  1925-1926  season  in  this  orchard  was  slight 
and  small-leaved.  This,  is  illustrated  by  figure  8,  which  shows  a  tree 
of  the  average  size  and  production  for  the  entire  field,  photographed 
in  1927.  At  the  end  of  the  ten-year  period  it  is  believed  that  some 
nutrient  materials  are  present  in  the  soil  in  such  low  concentrations 
that  they  are  beginning  to  limit  the  growth  and  productivity  of  the 
trees.  This  condition  makes  the  present,  therefore,  an  ideal  time  to 
commence  the  differential  treatments,  since  a  relatively  early  response 
to  beneficial  treatments  may  be  anticipated. 


18 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


OBSERVATIONS    REGARDING    THE    VARIATION    IN    THE    SIZE    AND 
PRODUCTIVITY   OF   THE   TREES 

TEUNK  MEASUREMENTS 

Records  have  been  made  annually  of  the  growth  of  the  trees. 
Trunk-circumference  measurements  have  been  made  during  the  whole 
period  since  the  trees  were  planted.  The  yearly  trunk  measurements 
have  been  at  the  same  position  on  the  trunk.  Each  tree  has  been 
marked  with  a  painted  band  showing  the  place  of  measurement.  The 
smallest  circumference  on  the  trunk  between  the  swell  of  the  branches 
and  the  swell  of  the  root  system  was  chosen  for  this  measurement. 
This  measurement  was  converted  into  area  of  cross  section.  Space 
will  not  permit  presenting  all  the  data  which  show  the  amount  of 
variation  among  all  the  individual  trees  for  each  year.  However,  an 
illustration  of  the  amount  of  variation  in  the  plots  is  shown  by  table  2, 
which  presents  the  average  trunk  size  per  tree,  in  each  plot,  in  1926. 


TABLE  2 
Average  Trunk  Measurement  pfr  Tree  in  each  Plot  for  1926 


Block 

Plot 

M 

L 

K 

1 
J 

I 

H 

G 

F 

E 

D 

A 

rea  of  cros 

s  section  in  square 

centimete 

rs 

2 

111 

109 

104 

117 

129 

132 

134 

4 

111 

114 

112 

105 

129 

134 

142 

6 

118 

114 

113 

107 

128 

121 

127 

8 

119 

113 

109 

129 

133 

130 

139 

10 

115 

120 

127 

123 

141 

135 

136 

12 

113 

125 

122 

117 

130 

135 

129 

14 

126 

121 

137 

120 

146 

153 

132 

128 

16 

122 

122 

131 

120 

135 

148 

103 

114 

18 

122 

117 

120 

127 

149 

136 

133 

131 

20 

115 

115 

126 

127 

143 

142 

128 

126 

22 

129 

122 

133 

127 

134 

140 

140 

129 

127 

24 

132 

* 

127 

124 

129 

137 

133 

118 

125 

26 

124 

126 

117 

131 

137 

128 

129 

128 

28 

127 

122 

141 

127 

123 

127 

134 

128 

30 

128 

121 

133 

139 

132 

127 

130 

137 

32 

120 

119 

128 

126 

138 

122 

129 

144 

132 

34 

114 

* 

135 

119 

139 

132 

135 

124 

125 

36 

122 

119 

133 

123 

133 

136 

137 

132 

126 

38 

107 

117 

114 

123 

122 

128 

136 

122 

125 

40 

128 

118 

134 

124 

118 

123 

126 

123 

130 

42 

118 

110 

120 

118 

136 

123 

131 

132 

128 

44 

112 

121 

132 

130 

113 

115 

127 

131 

133 

46 

118 

134 

147 

139 

48 

127 

132 

125 

126 

50 

131 

128 

128 

137 

52 

129 

134 

143 

138 

54 

135 

142 

* 

131 

*  Plots  omitted  because  of  injury  to  frees. 


Bul.  451 


FERTILIZER    TRIALS   IN    A    BEARING    CITRUS    GROVE 


19 


In  averaging  the  eight  trees  of  a  plot,  the  variation  in  the  individual 
trees  has  naturally  been  leveled  to  some  extent.  On  the  basis  of  the 
mean  size  of  the  trees  in  each  plot,  the  differences  are  greater  than 
would  be  expected,  when  the  care  spent  in  establishing  a  uniform 
grove  is  taken  into  consideration. 


Fig.  8. — Individual  Navel  orange  tree  of  average  size  and  production  at  time 
of  starting  the  fertilizer  trials,  1927.     (Tree  E-4-3.) 


The  trees  in  plot  E-16  are  among  the  smallest  in  trunk  cross- 
section  ;  those  in  plot  H-14  are  49  per  cent  larger.  The  measurements 
of  the  trees  in  these  plots  in  1918,  one  year  after  the  trees  were  planted 
in  the  orchard,  showed  that  plot  H-14  was  even  then  31  per  cent 
larger  than  plot  E-16. 

Apparently  the  chance  distribution  of  the  trees  at  the  time  the 
orchard  was  planted  accounts  in  a  large  degree  for  subnormal-sized 
trees  being  originally  grouped  together  in  plot  E-16.  In  addition  to 
this,  the  fact  that  this  plot  has  been  making  slower  growth  than 


20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


some  of  the  other  plots  leads  us  to  conclude  that  E-16  is  also  located 
on  soil  which  is  subnormal  in  productivity  in  comparison  with  many 
other  plots  of  the  field. 

It  seems  probable  that  the  present  range  in  plot  averages  of  tree 
size  could  have  been  materially  reduced  by  so  distributing  the 
different-sized  trees  at  the  time  of  planting  as  to  make  the  plot  aver- 
ages uniform  throughout  the  field.  The  distribution  of  the  trees  by 
pure  chance  might  be  expected  to  locate  a  group  of  either  exception- 
ally large  or  exceptionally  small  trees  in  the  same  plot  occasionally. 

VOLUME  OF  TOPS 
Top-volume  measurements  have  been  made  yearly  since  1921,  and 
have  been  recorded  in  cubic  feet.  The  measurements  over  and  around 
the  trees  have  been  taken  to  the  nearest  foot  by  means  of  a  fumigation 
tent,  and  the  cubic  contents  calculated  by  the  conventional  method 
used  in  determining  fumigation  dosage. 

TABLE  3 

Average  Top  Volume  per  Tree  in  each  Plot,  1926 


Block 

Plot 

M 

L 

K 

J 

I 

H 

G 

F 

E 

D 

A 

verage  top  volume  per  tree,  i 

n  cubic  fe 

et 

2 

733 

758 

757 

780 

927 

874 

868 

4 

725 

769 

868 

703 

858 

954 

921 

6 

845 

761 

815 

723 

947 

761 

829 

8 

776 

750 

784 

817 

934 

909 

1014 

10 

755 

777 

800 

869 

1014 

936 

936 

12 

735 

825 

818 

801 

926 

848 

814 

14 

853 

887 

876 

791 

921 

1115 

881 

783 

16 

812 

831 

888 

804 

855 

992 

596 

710 

18 

787 

827 

825 

803 

921 

917 

860 

895 

20 

699 

821 

935 

893 

945 

1001 

836 

811 

22 

803 

765 

891 

969 

995 

983 

901 

802 

871 

24 

764 

* 

857 

944 

858 

1005 

898 

761 

799 

26 

759 

799 

778 

819 

857 

979 

829 

889 

28 

862 

823 

863 

840 

863 

965 

973 

839 

30 

756 

754 

847 

887 

854 

930 

866 

877 

32 

799 

791 

799 

904 

845 

797 

918 

1071 

784 

34 

738 

* 

845 

780 

942 

866 

919 

916 

732 

36 

750 

790 

843 

•  848 

947 

901 

975 

976 

813 

38 

727 

801 

817 

771 

806 

807 

927 

747 

809 

40 

791 

819 

826 

867 

848 

878 

854 

865 

830 

42 

696 

730 

885 

822 

894 

882 

789 

905 

811 

44 

710 

813 

832 

850 

796 

851 

873 

896 

849 

46 

815 

885 

963 

944 

48 

843 

849 

901 

750 

50 

840 

840 

895 

924 

52 

829 

920 

1006 

847 

54 

855 

959 

* 

823 

*  Plots  omitted  because  of  injury  to  trees. 


BlJL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


21 


The  extent  of  the  variation  in  top  volume  between  the  several 
plots  is  shown  by  table  3.  This  presents  the  average  top  volume  per 
tree,  in  each  plot,  for  the  entire  grove  in  1926.  The  greatest  range 
in  variability  is  shown  in  comparing  plot  H-14  with  E-16  ;  the  former, 
with  an  average  top  volume  of  1,115  cubic  feet,  is  87  per  cent  larger 
than  the  latter  plot,  with  only  596  cubic  feet  as  an  average  top 
volume.     The  differences  in  top  volume  are  somewhat  larger  than  the 


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PLOT  NUMBERS 
Fig.  9. — Average  top  volume  per  tree  in  each  plot  of  Block  I,  1922-1926,  inclusive. 


extreme  range  in  variation  in  size  as  indicated  by  trunk  measurement. 
There  is,  however,  a  close  correlation  between  top  volume  and  trunk 
measurement. 

It  has  been  notable  that  the  differences  in  size  between  the  several 
plots  during  the  past  four  years  have  been  very  consistent  year  after 
year.  The  plots  which  included  trees  of  small  size  in  1921  as  a  rule 
still  have  relatively  small  trees  in  1926.  This  is  brought  out  by 
table  4,  which  shows  changes  in  the  top  volume  of  the  trees  for 
block  I  for  five  years.     The  data  are  shown  graphically  in  figure  9. 


22 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  linear  plotting  of  the  cubical  measurements  of  the  top  volume 
has  exaggerated  the  apparent  differences  in  the  volume  sizes  of  the 
plots  as  judged  by  visual  observation  in  the  field.  The  graphs  are 
presented  primarily  to  show  the  parallel  trend  of  the  growth  of  the 
plots  from  year  to  year  and  the  tendency  for  the  large  plots  to  remain 
relatively  large  while  the  small  plots  remain  consistently  small. 
Further  reference  to  this  subject  is  also  made  under  the  heading  of 
abnormal  trees  (see  p.  28).  This  tendency  has  some  exceptions,  as  is 
shown  by  plot  28,  block  I,  compared  with  plot  26,  block  I,  during 
1924  and  in  the  other  four  years.  Such  exceptions  in  the  trend  of 
growth  occur  in  only  a  small  minority  of  cases. 


TABLE  4 

Average  Top  Volume  Per  Tree  in  each  Plot  of  Block  I,  for  each  Year, 
1922-1926,  Inclusive 


Plot 

Year 

2 

4 

6 

8 

10 

12 

14 

16 

18 

20 

22 

24 

26 

28 

30 

32 

34 

36 

38 

40 

42 

44 

Average  top  volume  per  tree,  in  cubic  feet 

1922 

390 

365 

385 

387 

413 

391 

357 

375 

437 

398 

443 

391 

379 

389 

407 

393 

403 

407 

413 

405 

409 

399 

1923 

540 

518 

561 

533 

577 

548 

479 

482 

534 

534 

586 

496 

460 

497 

492 

530 

525 

528 

445 

497 

480 

448 

1924 

756 

667 

734 

702 

793 

673 

643 

655 

760 

743 

775 

649 

671 

634 

628 

663 

747 

729 

615 

663 

673 

629 

1925 

828 

754 

826 

775 

928 

793 

791 

726 

874 

847 

868 

786 

728 

742 

773 

739 

791 

772 

713 

751 

788 

754 

1926 

927 

858 

947 

934 

1014 

926 

921 

855 

920 

945 

995 

858 

857 

863 

854 

845 

942 

947 

806 

848 

894 

796 

PRODUCTION 

The  success  or  failure  of  the  future  fertilizer  treatments  will  be 
finally  judged  by  their  effect  upon  fruit  production.  The  yield 
records,  before  any  differential  treatments  were  started,  therefore 
become  of  greatest  interest  in  interpreting  the  future  observations. 
The  average  annual  production  per  tree  in  each  plot  for  a  six-year 
period  is  shown  in  table  5.  As  a  general  rule  the  largest  Navel  orange 
trees  have  also  been  the  most  productive,  although  there  are  notable 
exceptions  to  this  prevailing  tendency.  The  degree  of  variation  in  the 
yields  of  the  plots  has,  however,  been  even  greater  than  the  variation 
in  the  size  of  the  trees.  The  striking  variation  in  the  plot  yields  is  in 
harmony  with  other  studies  which  have  been  conducted  for  the  pur- 
pose of  determining  the  accuracy  of  plot  trials.6    There  is  a  difference 

o  Batchelor,  L.  D.,  and  H.  S.  Reed.  The  relation  of  the  variability  of  yields 
of  fruit  trees  to  the  accuracy  of  field  trials.    Jour.  Agr.  Res.  12:245-283.     1918. 


BUL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


23 


of  practically  109  per  cent  between  the  lowest  yielding  plot,  M-8, 
which  produced  an  annual  average  of  79  pounds  of  oranges  per 
tree  for  the  entire  six-year  period,  and  plot  F-44,  which  produced 
165  pounds  per  tree  annually  during  the  same  period.  The  two  plots 
showing  the  extremes  of  productivity  are  located  one-third  of  a  mile 
apart.  Such  a  variation  in  productivity  is  not  strange  in  comparing 
areas  of  soil  located  at  such  a  distance  from  each  other,  even  though 
they  are  a  part  of  a  block  of  land  which  has  been  treated  as  uniformly 
as  is  practicable.  A  comparison  of  adjacent  plots,  however,  shows 
varaitions  in  production  in  some  cases  of  30  to  40  per  cent.  This  is 
illustrated  by  referring  to  table  5  and  comparing  the  yields  of  the 
following  pairs  of  adjacent  plots :  E-16  and  E-14 ;  G-26  and  G-28 ; 
J-6  and  1-6 ;  and  M-22  and  L-22. 

TABLE  5 

Average  Annual  Yield  per  Tree  in  each  Plot  for  the  Six-year  Period,  1922 

to  1927,  Inclusive 


Block 

Plot 

M 

L 

K 

J 

I 

H 

G 

F 

E 

D 

I 

Lverage  ai 

mual  yiel 

:l  per  tree 

in  pounc 

Is 

2 

87 

103 

96 

103 

113 

100 

121 

4 

95 

106 

110 

104 

120 

127 

140 

6 

111 

110 

109 

99 

140 

116 

141 

8 

79 

112 

99 

115 

129 

139 

137 

10 

98 

113 

116 

110 

122 

130 

128 

12 

102 

109 

122 

128 

113 

140 

133 

14 

93 

126 

137 

128 

108 

132 

133 

138 

16 

100 

116 

129 

119 

113 

130 

100 

107 

18 

93 

115 

112 

119 

120 

132 

124 

105 

20 

98 

116 

127 

135 

125 

131 

116 

105 

22 

98 

138 

132 

137 

138 

116 

120 

122 

124 

24 

103 

* 

121 

119 

115 

114 

123 

118 

121 

26 

97 

121 

104 

110 

117 

115 

103 

130 

28 

119 

119 

129 

132 

129 

138 

141 

116 

30 

108 

131 

148 

130 

152 

153 

140 

136 

32 

127 

127 

135 

134 

126 

129 

133 

152 

139 

34 

119 

* 

140 

134 

121 

139 

135 

128 

128 

36 

135 

147 

146 

147 

150 

143 

127 

138 

136 

38 

120 

137 

119 

124 

136 

142 

148 

129 

133 

40 

121 

138 

135 

139 

142 

150 

133 

131 

122 

42 

114 

128 

157 

146 

144 

142 

155 

153 

138 

44 

107 

126 

143 

135 

126 

140 

144 

165 

144 

46 

126 

155 

155 

146 

48 

129 

150 

140 

117 

50 

134 

142 

131 

115 

52 

114 

150 

149 

122 

54 

114 

136 

* 

108 

Plots  omitted  because  of  injury  to  trees. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  persistent  tendency  for  high  or  low-yielding  plots  to  remain 
in  the  same  respective  class  is  illustrated  by  figure  6  (page  15).  This 
figure  shows  the  average  annual  production  per  tree  in  each  plot  of 
block  I  during  the  six-year  period.  Plots  which  are  high  producers 
on  year  apparently  tend  to  be  high  other  years,  while  in  general  low- 
producing  plots  have  been  consistently  low  in  yield.  Plot  32,  for 
example,  has  each  year  consistently  produced  less  than  plot  30,  and 
plot  34  has  consistently  produced  less  than  plot  36  during  the  same 
period. 

TABLE   6 

Mean  Yearly  Yield  per  Tree  in  each  Block 

(In  pounds) 


Block 

1922 

1923 

1924 

1925 

1926 

1927 

D       

64.8 
56.3 
91.9 
89.1 
96.6 
92.5 
93.2 
87.9 
85.2 
68.5 

76.0 
78.7 
68.1 
77.1 
68.1 
73.5 
75.7 
75.3 
73  1 
66  0 

165.0 

166.2 
173.8 
179.7 
170.3 
162  0 
156.9 
155  1 
146  1 
126.6 

133  0 

134  0 
168.3 
154.4 
151.2 
144.6 
142  4 
142 .6 
139.2 
120  4 

141  9 
122  2 
166.2 
148.4 
12C.1 
121  0 
121  5 
121  4 
116  6 
101  4 

181.0 

E 

174  5 

F         

187.5 

G 

174.8 

H  

183  0 

I 

169.0 

J 

158  8 

K  . 

174.5 

L 

171.3 

M 

150  0 

The  two  groups  of  factors  which  are  most  persistently  operative 
in  causing  the  variation  in  production  are :  first,  the  inherent  qualities 
of  the  tree  due  to  character  and  vigor  of  rootstock  and  top ;  second, 
the  variability  of  the  productivity  of  the  soil  in  one  part  of  the  field 
compared  with  another.  In  considering  the  yields  on  the  basis  of  the 
average  production  per  plot  of  eight  trees  each,  the  extremes  of  varia- 
bility among  individual  trees  are  largely  compensated  for.  The 
leveling  effect  of  averaging  the  yields  of  the  eight  trees  in  each  plot 
over  a  six-year  period  makes  it  possible  for  this  average  figure  to  be 
used  as  a  fairly  reliable  index  of  the  natural  productivity  of  the 
soil  on  which  the  respective  plots  are  located.  Inasmuch  as  the  indi- 
vidual trees  were  distributed  purely  by  chance  over  the  entire  field, 
it  seems  reasonable  to  believe  that  the  consistency  for  high  and  low 
production  among  plots  as  illustrated  by  block  I,  is  due  primarily  to 
variations  in  the  productivity  of  the  soil. 

This  interpretation  of  the  relative  importance  of  the  two  groups 
of  factors  causing  the  variation  in  the  average  production  of  plots  is 
further  substantiated  by  considering  the  average  production  of  the 
several  blocks  as  units,  over  the  six-year  period.    These  data  are  pre- 


BUI/.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  25 

sented  ill  table  6,  which  shows  a  relatively  consistent  tendency  for 
different  blocks  in  the  field  to  be  high  or  low  producers.  In  this  case 
each  block  is  represented  by  the  average  yield  of  eleven  or  more  plots ; 
thus  the  variability  of  88  or  more  trees  is  leveled  by  their  average, 
which  indicates  the  production  of  each  respective  block. 

Figure  7  shows  the  same  data  graphically.  Prom  this  it  is  clearly 
seen  that  the  relative  productivity  of  the  respective  blocks  is  not 
absolutely  consistent  from  year  to  year,  but  there  is  nevertheless  a 
marked  tendency  for  the  highest-yielding  blocks,  such  as  F  and  G, 
to  remain  so  throughout  the  period,  and  the  lowest-yielding,  block  M, 
to  continue  as  such. 

In  allocating  the  ultimate  unit  plots  for  each  respective  fertilizer 
treatment,  an  attempt  has  been  made  to  use  differences  in  the  prod  ac- 
tive capacity  of  different  portions  of  the  field  as  one  factor  in  reach- 
ing a  decision  on  this  subject.  With  a  previous  knowledge  of  the 
magnitude  of  relative  differences  between  all  plots,  the  four  repeti- 
tions of  a  given  treatment  may  be  so  arranged  that  each  treatment 
may  be  tried  on  plots  the  summation  yield  of  which,  prior  to  the 
start  of  the  experiments,  is  approximately  equal  to  that  of  the  summa- 
tion yield  of  the  plots  of  other  treatments,  By  this  method  all  treat- 
ments may  be  tried  on  an  equal  footing,  without  being  handicapped 
or  favored  by  being  located  on  plots  the  summation  yield  of  which  is 
excessively  low  or  high.  This  procedure  may  materially  reduce  the 
experimental  error  inherent  in  the  trials,  provided  the  differences 
which  are  apparent  at  the  beginning  of  the  fertilizer  trials  prove  to 
be  consistent  to  some  degree.  Provision  has  been  made  to  study  the 
degree  of  consistency  exhibited  in  the  future,  in  comparison  with  the 
first  six-year  period.  This  aspect  of  the  problem  will  be  discussed 
in  a  following  section. 

ATTEMPTS  TO  DETERMINE  CAUSES  OF  VARIATION 

The  underlying  causes  of  the  persistent  variation  in  the  produc- 
tion of  individual  trees  and  plots  which  must  be  considered  normal 
for  this  orchard  are  probably  very  complex,  and  beyond  a  full  explan- 
ation at  this  time.  A  more  complete  knowledge  of  the  factors  involved 
would  be  of  inestimable  value  in  planning  an  experiment  such  as  that 
which  is  now  being  initiated.  It  would  also  be  a  great  aid  in  the 
future  interpretation  of  the  effects  of  specific  treatments. 

Several  attempts  have  been  made  to  determine  the  fundamental 
causes  of  the  varying  performance  of  individual  trees  and  of  indi- 
vidual plots.    Soil  surveys  have  been  conducted  at  two  distinct  periods 


26  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

throughout  the  orchard.  Borings  were  made  to  a  depth  of  4  feet  in 
the  tree  holes  at  the  time  of  planting.  At  a  later  date  composite  soil 
samples  were  taken  in  each  plot  to  a  depth  of  6  feet.  The  moisture 
retentiveness  of  the  soil  in  the  root  zone  of  the  orange  trees  has  been 
determined  in  a  large  section  of  the  field,  and  has  been  studied  in 
relation  to  the  growth  and  yield  of  the  trees  in  that  area.  The  amount 
of  moisture  in  the  soil  of  certain  representative  plots  has  been  deter- 
mined over  a  considerable  period  of  time.  This  has  been  studied  with 
regard  both  to  the  absolute  amount  of  moisture  and  to  the  amount 
theoretically  available  to  the  tree,  as  indicated  by  the  wilting  coeffi- 
cient of  the  soil  in  those  plots.  The  total  amounts  and  the  seasonal 
distribution  of  nitrates  in  the  soil  have  also  been  studied  in  high  and 
low-yielding  plots.  Individual  trees  have  been  inspected  for  differ- 
ences in  relative  infestation  of  various  parasites,  particularly  the 
citrus  nematode,  Tylenchulus  semipenetrans.  In  addition,  all  of  the 
trees  in  the  plots  showing  the  greatest  extremes  of  production  have 
been  examined  for  abnormalities  in  the  distribution  of  the  main  roots 
for  a  distance  of  about  one  foot  from  the  trunk  of  the  tree. 

However,  none  of  the  factors  enumerated  appear  to  be  the  prim- 
ary cause  of  the  differences  in  the  yield  performances  which  have  been 
observed.  The  varying  behavior  of  individual  normal  trees,  and  espe- 
cially of  individual  plots  and  larger  areas  under  conditions  of  uniform 
culture,  must  be  due  to  certain  factors  or  combinations  of  factors 
which  have  not  yet  been  brought  to  light,  and  apparently  for  want 
of  a  better  explanatory  term,  may  be  described  only  in  the  most 
general  way  as  the  variability  in  the  productivity  of  the  soil.  Con- 
tinued study  of  this  subject  may  be  productive  of  more  specific 
information. 

VARIATION    IN    COMPARISON    WITH    THAT    OF    AVERAGE    GROVES 

In  spite  of  the  variations  in  the  growth  and  production  of  the  trees 
of  this  field  which  have  been  cited,  it  is  believed  that  this  planting 
is  singularly  uniform  in  comparison  with  the  average  citrus  grove. 
This  fact  has  been  brought  out  in  statistical  studies  of  the  variability 
of  this  and  other  orchards.  In  appearance  the  trees  are  strikingly 
similar.  This  relative  uniformity  is  shown  by  figure  10,  which  repre- 
sents a  view  of  the  grove  taken  in  1927  from  the  same  point  and 
looking  in  the  same  direction  as  was  figure  3,  taken  in  1917.  The 
appearance  of  the  trees  along  the  pipe  line  of  block  D  in  1927,  as 
shown  by  figure  11,  also  illustrates  the  uniformity  of  the  trees.  Figure 
11  also  shows  the  relation  of  the  standpipes  to  the  trees,  and  the 
marking  of  the  individual  treatment  plots. 


Bul,  451 


FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


27 


Fig.   10. — View  of  grove  in   1927   showing  relative  uniformity   of  trees.     This 
view  taken  from  the  same  location  as  that  shown  in  figure  3. 


Fig.  11. — Appearance  of  trees  along  the  pipe  line  of  block  D,  in  1927, 
showing  uniformity  of  growth. 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


ABNORMAL  TREES 

The  trees  in  this  orchard  have  passed  through  most  of  the  ordinary 
vicissitudes  of  a  commercial  orchard.  As  might  be  expected  at  the 
end  of  the  first  ten-year  period,  there  are  certain  trees  which  are 
clearly  subnormal  in  their  growth  and  production.  The  yields  and 
the  growth  records  of  such  trees  have  not  been  included  in  the  average 
yields.  When  four  or  more  trees  in  any  one  plot  are  known  to  be 
abnormal  the  records  for  the  entire  plot  have  been  discarded. 


TABLE   7 

Comparative  Sizes  of  Normal  and   Subnormal   Trees   One  Year  After 
Planting  and  Eight  Years  Later, 


Area  of  cross  section  of  trunk 

Plot  in  which 
abnormal  tree 

1918 

1926 

is  located 

Subnormal  tree 
sq.  cm. 

Average  of 

two  adjacent 

normal  trees 

sq.  cm. 

Subnormal  tree 
sq.  cm. 

Average  of  two 

adjacent  normal  trees 

in  same  plot 

sq.  cm. 

D-40 

4  44 

5  05 
3.55 
3.04 
3.23 
4.08 
3  23 

6  10 
6  45 
6  01 
7.94 
6.41 
5.91 
6  31 

85.6 

99.2 
106.0 

77.5 
108.4 
100.  C 

74.0 

134.5 

F-44 

121.5 

K-36 

126.9 

L-  6 

120.3 

L-16 

120.5 

L-18 

112.8 

L-22 

129.7 

The  causes  of  most  of  the  subnormal  conditions  of  individual  trees 
are  clearly  apparent.  Such  trees  are  most  commonly  isolated  and 
have  therefore  not  destroyed  the  usefulness  of  the  remainder  of  the 
plot.  The  plots  in  such  cases  have  been  reduced  to  seven  trees.  In 
only  three  instances  have  whole  plots  been  discarded ;  in  these 
instances  four  or  more  of  the  trees  in  a  single  plot  were  injured  to 
some  degree  by  pocket  gophers  during  the  winter  of  1919-20.  At 
that  time  the  grove  was  being  given  ordinary  commercial  culture  and 
had  not  been  assigned  to  any  one  for  statistical  study.  The  trees 
injured  most  severely  were  pulled  out  and  young  trees  were  planted 
in  their  places.  Others,  less  severely  injured  by  gophers,  have  been 
inarched  with  four  seedlings  per  tree.  Some  of  these  have  entirely 
recovered  and  may  be  considered  normal  trees  at  the  present  time. 
Others  must  clearly  be  maintained  several  years  longer  before  their 
yield  can  be  used  in  connection  with  the  fertilizer  trials. 


BUL.  451 J  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


29 


Among"  the  1,592  Washington  Navel  trees  which  were  planted  as 
test  trees,  7  trees  are  clearly  subnormal  for  unknown  reasons.  It  is 
possible  that  they  are  on  inferior  rootstocks,  although  this  can  not  be 
proved  at  the  present  time.  The  selection  of  the  trees  which  was 
made  at  the  time  the  grove  was  planted  was  based  upon  the  judgment 
of  the  foreman  of  operations.     No  actual  measurements  of  the  trees 


Fig.  12. — Subnormal  tree  showing  small  size  of  tree  in  1927  (Tree  L-18-4). 

were  made,  and  no  attempt  was  made  to  have  the  average  size  of  the 
trees  in  each  plot  the  same.  From  records  taken  in  May  1918,  it  is 
clear  that  all  of  the  trees  which  are  subnormal  at  the  present  time 
were  smaller  than  the  average  trees  in  the  respective  plots  at  the 
time  the  grove  was  planted.  Table  7  gives  the  past  and  present  sizes 
of  subnormal  trees  compared  with  the  average  of  the  two  adjacent 
normal  trees  in  their  respective  plots.  The  small  size  of  the  subnormal 
trees  is  illustrated  by  the  one  shown  in  figure  12,  which  has  been 
photographed  on  the  same  scale  as  the  normal  tree  shown  in  figure  8. 


30 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


It  is  plain  from  table  7  that  the  seven  trees  therein  considered  are 
subnormal  in  vigor  and  have  been  so  from  the  time  they  were  planted 
in  the  orchard.  This  is  further  emphasized  by  table  8,  which  compares 
the  yield  of  the  subnormal  trees  with  the  average  yield  of  the  two 
adjacent  trees  for  each  year,  1921  to  1927,  inclusive. 


TABLE  8 

Yield  of  Subnormal   Trees  and  Average  Yield  of   Two   Adjacent   Normal 
Trees  in  the  Same  Plot  for  each  of  Seven  Years,  1921  to  1927,  Inclusive 

(In  pounds) 


Plot 

1921 

1922 

1923 

1924 

1925 

1926 

1927 

in  which 

abnormal 

tree  is 

located 

Sub- 
nor- 
mal 

Nor- 
mal 

Sub- 
nor- 
mal 

Nor- 
mal 

Sub- 
nor- 
mal 

Nor- 
mal 

Sub- 
nor- 
mal 

Nor- 
mal 

Sub- 
nor- 
mal 

Nor- 
mal 

Sub- 
nor- 
mal 

Nor- 
mal 

Sub- 
nor- 
mal 

Nor- 
mal 

D-40 

0 

2 

13 

36 

2 

75 

51 

187 

41 

139 

68 

116 

* 

138 

F-44 

4 

32 

13 

119 

14 

87 

184 

29 

187 

24 

195 

13 

207 

K-36 

4 

16 

132 

64 

39 

72 

49 

168 

28 

173 

78 

142 

128 

187 

L-  6 

4 

36 

8 

98 

12 

68 

41 

123 

44 

150 

19 

73 

24 

160 

L-16 

8 

32 

4 

98 

45 

59 

50 

152 

20 

134 

0 

73 

18 

161 

L-18 

4 

34 

34 

102 

25 

61 

78 

125 

64 

135 

19 

87 

15 

195 

L-22 

2 

34 

51 

100 

48 

119 

62 

184 

42 

142 

0 

107 

20 

178 

*  Special  treatment  of  tree  interfered  with  accuracy  of  record 

In  the  present  condition  of  the  subnormal  trees,  their  yields  cannot 
properly  be  used  in  computing  the  average  yields  for  the  respective 
plots  to  which  they  belong.  If  they  do  not  respond  to  the  inarching 
which  has  been  performed  on  them  and  make  a  more  nearly  normal 
growth,  they  may  soon  be  removed  and  the  space  replanted  to  young 
trees. 


VARIATION    IN   THE   YIELDS  OF  THE   PLOTS   IN    RELATION   TO 
PLANNING  THE  FUTURE  FERTILIZER  TRIALS 

NUMBER  OF  TREES  FOR  EACH  TREATMENT 

With  such  great  variation  in  the  yields  of  the  plots  as  is  evident 
from  table  5,  it  becomes  a  matter  of  important  consideration  to 
arrange  the  fertilizer  trials  of  the  future  so  that  each  treatment  will 
have  as  nearly  as  practicable  an  opportunity  to  be  fairly  tested. 
Statistical  studies  made  in  other  orange  groves  have  indicated  that  it 
is  desirable  to  have  a  minimum  of  thirty-two  trees  assigned  to  each 
fertilizer  treatment.  This  grove  was  planned  in  such  a  way  that  this 
number  might  be  used. 


BUL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


31 


EFFECT  OF  GROUPING  ALL  LIKE-TREATED  TREES  TOGETHER 

Many  fertilizer  experiments  have  been  conducted  during1  the  past 
two  decades  in  which  comparisons  were  made  between  two  differently 
treated  plots,  without  including  any  repetitions  of  the  treatments  in 
several  parts  of  the  experimental  field.  In  accordance  with  the  laws 
of  simple  sampling,  however,  the  division  of  a  treatment  among  two 
or  more  ultimate  unit  plots  located  in  different  parts  of  the  field  may 
be  expected  to  give  greater  accuracy  in  determining  the  value  of  a 
treatment  than  if  the  given  treatment  had  been  applied  to  the  same 
number  of  ultimate  unit  plots  located  adjacent  to  each  other.  A  study 
of  the  yield  records  of  the  field  of  Navel  oranges  discussed  here  will 
illustrate  the  principle  involved. 


TABLE  9 

The  Average  Annual  Yields  Per  Tree  of  the  Ultimate  Unit  Plots  of  Forty- 
nine  Theoretical  Treatments  and  the  Average  of  Groups  of 
Four  such  Plots  Arranged  Adjacent  to  each  other 


Yield  in  pounds 

Treat- 
ment 
No. 

Yield  in  pounds 

Treat- 
ment 
No. 

Of 

ultimate  unit  plots 

Average 
for 
treat- 
ment 

Of  ultimate  unit  plots 

Average 
for 
treat- 
ment 

1 

121 

140 

141 

137 

135 

26 

117 

129 

152 

126 

131 

2 

128 

133 

138 

107 

127 

27 

121 

150 

136 

142 

137 

3 

105 

105 

124 

121 

114 

28 

144 

126 

103 

104 

119 

4 

130 

116 

136 

139 

130 

29 

99 

115 

110 

128 

113 

.5 

128 

136 

133 

122 

130 

30 

128 

119 

119 

135 

125 

6 

138 

144 

146 

117 

136 

31 

137 

119 

110 

132 

125 

7 

115 

122 

108 

100 

111 

32 

130 

134 

134 

147 

136 

8 

127 

116 

139 

130 

128 

33 

124 

139 

146 

135 

136 

9 

140 

133 

100 

124 

124 

34 

96 

110 

109 

99 

104 

10 

116 

122 

118 

152 

127 

35 

116 

122 

137 

129 

126 

11 

128 

138 

129 

131 

132 

36 

112 

127 

132 

121 

123 

12 

153 

165 

155 

140 

153 

37 

104 

129 

148 

135 

129 

13 

131 

149 

120 

123 

131 

38 

140 

146 

119 

135 

135 

14 

103 

141 

140 

133 

129 

39 

157 

143 

103 

106 

127 

15 

135 

127 

148 

133 

136 

40 

110 

112 

113 

109 

111 

16 

155 

144 

155 

150 

151 

41 

126 

116 

115 

116 

118 

17 

142 

150 

136 

132 

140 

42 

138 

121 

119 

131 

127 

18 

130 

132 

131 

116 

127 

43 

127 

147 

137 

138 

137 

19 

114 

115 

138 

153 

130 

44 

128 

126 

87 

95 

109 

20 

129 

139 

143 

142 

138 

45 

111 

79 

98 

102 

98 

21 

150 

142 

140 

126 

140 

46 

93 

100 

93 

98 

96 

22 

129 

134 

114 

114 

123 

47 

98 

103 

97 

119 

104 

23 

113 

120 

140 

129 

126 

48 

108 

127 

119 

135 

122 

24 

122 

113 

108 

113 

114 

49 

120 

121 

114 

107 

116 

25 

120 

125 

138 

115 

125 

32 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Discarding  3  abnormal  plots,  there  remain  196  plots  of  practically 
8  trees  each  in  the  entire  field.  If  4  of  these  plots  are  assigned  to 
each  treatment,  making  a  total  of  32  trees,  in  harmony  with  previous 
study,  it  is  possible  to  try  49  treatments  in  the  experiment.  Let  us 
assume  that  each  of  these  theoretical  treatments  is  located  on  4  con- 
tiguous plots.  The  average  yield  for  these  4  plots  now  becomes  the 
average  yield  for  the  given  treated  area.  Table  9  shows  the  results 
obtained  in  this  field  by  combining  adjacent  plots  in  this  way.  The 
extremes  of  production  of  the  summation  plots  show  a  range  in 
average  annual  yield  per  tree  of  from  96  to  153  pounds.  During  the 
six-year  period  the  high-yielding  group  of  4  plots  produced,  therefore, 
practically  60  per  cent  more  fruit  than  the  low-yielding  group.  This 
error  might  have  been  extremely  misleading  had  the  plots  been  under 
different  cultural  or  fertilizer  conditions,  and  might  have  frustrated 
all  attempts  to  draw  accurate  conclusions  as  to  the  effect  of  the 
treatments. 

TABLE  10 
The  Average  Annual  Yields  Per  Tree  of  the  Ultimate  Unit  Plots  or  Forty- 
nine  Theoretical  Treatments  and  the  Averages  of  Groups  of 
Four  of  such  Plots  Scattered  at  Regular  Intervals 


Yield  in  pounds 

Treat- 
ment. 

No. 

Yield  in  pounds 

Treat- 
ment 

No. 

Of  ultimate  unit  plots 

Average 
for 
treat- 
ment 

Of  ultimat 

e  unit  plots 

Average 
for 
treat- 
ment 

1 

121 

143 

138 

135 

136 

26 

122 

138 

132 

128 

130 

2 

140 

120 

115 

140 

129 

27 

108 

153 

130 

126 

129 

3 

141 

123 

117 

146 

132 

28 

100 

129 

134 

87 

138 

4 

137 

103 

123 

119 

122 

23 

127 

139 

134 

95 

124 

5 

128 

141 

152 

135 

139 

30 

116 

143 

147 

111 

129 

6 

133 

140 

126 

157 

133 

31 

139 

142 

124 

79 

121 

7 

138 

133 

121 

143 

134 

32 

130 

150 

139 

98 

129 

8 

107 

135 

150 

103 

124 

33 

140 

142 

146 

102 

133 

9 

105 

127 

136 

106 

119 

34 

133 

140 

135 

93 

125 

10 

105 

148 

142 

110 

126 

35 

100 

126 

96 

100 

106 

11 

124 

133 

144 

112 

128 

36 

124 

129 

110 

93 

114 

12 

121 

155 

126 

113 

123 

37 

116 

134 

103 

98 

114 

13 

130 

144 

103 

109 

122 

38 

122 

114 

99 

98 

108 

14 

116 

155 

104 

126 

125 

39 

118 

114 

116 

103 

113 

15 

136 

150 

99 

116 

125 

40 

152 

113 

122 

97 

121 

16 

139 

142 

115 

115 

128 

41 

128 

120 

137 

119 

126 

17 

128 

150 

110 

116 

126 

42 

138 

140 

129 

108 

123 

18 

136 

136 

128 

138 

135 

43 

123 

129 

112 

127 

124 

19 

133 

132 

128 

121 

129 

44 

131 

122 

127 

119 

125 

20 

122 

130 

119 

119 

123 

45 

153 

113 

132 

135 

133 

21 

138 

132 

119 

131 

130 

46 

165 

108 

121 

120 

129 

22 

144 

131 

135 

127 

134 

47 

155 

113 

104 

121 

123 

23 

146 

116 

137 

147 

137 

48 

140 

120 

129 

114 

126 

24 

117 

114 

119 

137 

122 

49 

131 

125 

148 

107 

128 

25 

115 

115 

110 

138 

120 

BUL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  33 

EFFECT  OF  SCATTERING  TREATMENT  PLOTS 

If,  on  the  other  hand,  4  repetitions  of  each  of  the  49  different 
theoretical  treatments  are  distributed  at  regular  intervals  throughout 
the  field,  instead  of  being  located  adjacent  to  each  other,  we  might 
theoretically  expect  a  reduction  of  this  error.  Table  10  shows  the 
results  obtained  when  this  is  done.  This  table  gives  the  yields  of  each 
of  4  plots  chosen  in  regular  numerical  rotation  along  each  block  and 
also  the  average  annual  yield  per  tree  of  the  summation  plot  for  each 
theoretical  treatment.  According  to  this  arrangement  the  49  theo- 
retical treatments  show  a  range  in  average  annual  yield  per  tree  of 
from  106  to  139  pounds.  With  this  distribution,  therefore,  the  high- 
yielding  group  of  plots  has  produced  31  per  cent  more  fruit  during 
the  six-year  period  than  the  low-yielding  group  of  plots. 

It  is  plain  from  the  above  calculations  that  even  the  scattering  of 
4  unit  plots  at  regular  intervals  throughout  the  field,  does  not  suffi- 
ciently reduce  the  differences  between  the  theoretically  treated  plots. 
Conclusions  have  frequently  been  drawn,  and  recommendations  have 
often  been  made,  from  field  trials  conducted  in  the  past  when  the 
differences  were  substantially  less  than  30  per  cent.  The  studies  of 
many  investigators  have  pointed  out  this  source  of  error  in  field  trials 
as  being  attributable  to  the  varying  productivity  of  the  soil.  It  is 
clear  that  some  other  method  of  combining  the  ultimate  unit  plots, 
into  a,  more  equal  summation  yield  for  a  given  treatment,  is  necessary. 
Otherwise  only  very  large  differences,  of  50  per  cent  or  more,  between 
respective  treatments  repeated  in  numerical  series  as  above  could  be 
considered  significant  in  the  trials  which  are  planned  for  this 
experiment. 

ARRANGEMENT   OF  PLOTS   ON   BASIS   OF   PRODUCTIVITY 

The  limitation  of  the  accuracy  of  chance  distribution  of  a  par- 
ticular treatment,  repeated  a  small  number  of  times  has  pointed  to 
the  advisability  of  a  different  arrangement.  The  tendency  which 
has  been  indicated  to  date  for  either  high  or  low-yielding  plots  to 
continue  so,  has  prompted  the  arrangement  of  the  differential  treat- 
ments in  this  field  on  the  basis  of  their  productivity.  If  the  variations 
in  the  productivity  of  different  portions  of  the  field  under  considera- 
tion are  consistent  year  after  year,  or  even  partially  so,  as  the  data 
which  have  been  obtained  seem  to  indicate,  there  should  be  a  reduc- 
tion in  the  error  of  the  field  trials  herein  proposed  by  a  distribution 
of  the  ultimate  unit  plots  in  full  consideration  of  the  knowledge  of  the 
differences  which  exist. 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Means  of  Determining  Reliance  to  be  Placed  on  Yields  Prior  to  the 
Start  of  the  Experiment. — The  degree  of  reliance  which  can  be  placed 
upon  the  apparent  productivity  of  the  individual  plots,  as  indicated 
by  the  yields  of  six  years,  may  possibly  decrease  in  the  future.  This 
possibility  will  be  subject  to  further  study.  As  a  result  of  the  observa- 
tions to  be  made,  it  may  be  possible  to  bring  any  changes  in  the  degree 
of  reliance  of  these  records  to  bear  upon  the  comparisons  to  be  made 
between  differently  treated  plots. 

For  the  purpose  of  measuring  the  reliability  of  the  index  of  rela- 
tive yield,  as  here  used,  25  of  the  196  utilizable  plots  will  continue  to 
be  devoted  to  statistical  study  bearing  on  this  question.  This  group 
of  25  plots  will  have  uniform  fertilizer  and  cultural  treatment.  These 
plots  have  been  selected  arbitrarily  with  regard  to  a  presumably  satis- 
factory geographical  distribution,  and  also  in  such  a  way  that  their 
yields  fairly  represent  the  extremes  of  variation  in  the  field,  yet  their 
average  yield  is  equal  to  that  of  the  entire  field.  In  addition,  each 
particular  plot  has  been  selected  so  that  its  previous  yield  is  equal  to 
the  average  yield  of  a  definite  area  of  plots  adjacent  to  it.  They  will, 
therefore,  serve  as  indices  of  the  effect  of  future  seasons  and  growth 
upon  individual  plots  and  upon  the  local  areas  about  them,  as  well  as 
upon  the  field  as  a  whole.  In  this  way  they  may  be  reliable  guides  as 
to  the  validity  of  the  use  of  a  priori  records  in  planning  the  field 
trials  herein  described. 

Method  of  Distributing  Treatment  Plots. — After  the  twenty-five 
plots  just  discussed7  have  been  distributed  throughout  the  field,  there 
remain  168  plots  which  may  be  used  for  42  trials  of  4  plots  each. 
The  treatments  have  been  so  distributed  that  each  will  be  located  on 
a  group  of  4  ultimate  unit  plots,  the  summation  yield  of  which  has 
been  approximately  equal  to  the  summation  yield  of  the  group  of  plots 
devoted  to  each  other  treatment. 

The  method  which  has  been  used  to  effect  the  equalization  of  the 
yielding  capacity  of  each  group  of  4  plots  devoted  to  each  treatment 
is  as  follows.  The  observed  yields  of  the  individual  plots  were 
arranged  in  order  of  their  descending  value.  The  list  was  then 
divided  into  quartans.  The  four  quartans  of  plots  may  be  designated 
as  good,  medium,  low  and  poor  yielding.  If  each  treatment  is  dis- 
tributed with  one  plot  in  each  quartan,  the  summation  yields  for  all 
treatments  becomes  approximately  equal.  The  yields  arbitrarily  com- 
bined in  this  way  are  set  forth  in  table  11,  stated  as  the  average 
yearly  production  per  tree  for  each  combination  of  plots, 

7  In  addition  to  the  before-mentioned  25  plots,  3  plots  were  eliminated  for  the 
purpose  of  using  them  for  demonstration  work.  Plots  F54,  L24,  and  L34  are  dis- 
carded, as  j>reviously  noted,  because  of  pockot-gopher  injury  to  the  trees. 


BUL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


35 


TABLE  11 

The  Average  Annual  Yields  Per  Tree  of  the  Ultimate  Unit  Plots  of  Forty- 
two  Theoretical  Treatments  and  the  Average  of  Groups  of 
Four  such  Plots  Arranged  on  the  Basis  of  Yield 
and  other  Factors 


Yield  in  pounds 

Treat- 
ment 

No. 

Yield  in  pounds 

Treat- 
ment 

No. 

Of 

ultimate  unit  plots 

Average 
for 
treat- 
ment 

Of 

ultimate  unit  plots 

Average 
for 
treat- 
ment 

1 

148 

126 

124 

105 

126 

22 

139 

130 

120 

116 

126 

2 

139 

129 

124 

111 

126 

23 

146 

138 

115 

103 

126 

3 

135 

133 

116 

116 

125 

24 

144 

133 

115 

112 

126 

4 

155 

130 

119 

100 

126 

25 

155 

122 

117 

108 

126 

5 

153 

135 

122 

93 

126 

26 

153 

128 

115 

103 

125 

6 

138 

133 

129 

104 

126 

27 

137 

126 

122 

120 

126 

7 

139 

128 

119 

116 

126 

28 

137 

132 

122 

110 

125 

8 

140 

126 

119 

116 

125 

29 

165 

146 

113 

79 

126 

9 

144 

133 

115 

110 

126 

30 

152 

136 

114 

96 

125 

10 

150 

128 

121 

100 

125 

31 

150 

129 

119 

105 

126 

11 

142 

137 

127 

100 

127 

32 

136 

135 

121 

112 

126 

12 

150 

121 

119 

113 

126 

33 

135 

128 

127 

114 

126 

13 

142 

141 

122 

97 

126 

34 

147 

136 

114 

106 

126 

14 

139 

134 

119 

108 

125 

35 

138 

135 

128 

98 

125 

15 

148 

146 

120 

93 

127 

36 

140 

135 

125 

104 

126 

16 

157 

132 

131 

87 

127 

37 

142 

128 

126 

108 

126 

17 

155 

132 

121 

98 

127 

38 

147 

129 

119 

103 

125 

18 

140 

131 

129 

102 

126 

39 

141 

132 

119 

107 

125 

19 

152 

138 

116 

98 

126 

40 

140 

138 

127 

99 

126 

20 

134 

131 

124 

110 

125 

41 

150 

130 

126 

99 

126 

21 

142 

140 

114 

109 

126 

42 

140 

136 

118 

113 

127 

By  this  method  the  grouping  of  the  plots  to  be  used  for  individual 
fertilizer  treatments  has  been  accomplished  in  such  a  way  that  their 
average  yields  per  tree  prior  to  the  start  of  the  experiments  are 
approximately  the  same,  and  within  a  very  narrow  range  are  equal  to 
the  average  production  per  tree  of  the  entire  field.  The  table  indicates 
that  the  average  yearly  production  per  tree  for  the  highest-yielding 
group  of  plots  is  127  pounds,  while  the  average  for  the  lowest- 
producing  group  is  125  pounds.  By  this  arrangement8  the  best- 
yielding  group  has  produced  1.6  per  cent  more  fruit  than  the  lowest 
yielding.    This  difference  is  practically  negligible  in  trials  of  this  sort. 

This  arrangement  was  adopted  in  order  that  the  greatest  accuracy 
of  comparison  might  be  attained  by  the  customary  statistical  methods. 

s  In  choosing  the  plots  from  each  class  to  be  used  for  a  given  treatment  a 
particular  effort  was  made,  at  the  same  time,  to  so  locate  them  that  the 
various  repetitions  of  each  treatment  would  be  scattered  satisfactorily  from 
the  point  of  view  of  variations  in  soil  type,  visual  comparisons  of  .contrasting 
treatments,  ease  of  culture,  and  adequate  geographical  distribution. 


P'ot     A/t//n/>eAS 

Z    4   6     8   /O   tZ  M  /€   /S  ZO  Z2  24  Z6  Z8  30  Si  34  36  38  40  41  44  4*  48  SO  St  S+ 


40 


35 


41 


20 


3( 


42 


30 


37 


34 


it  a 


24 


26 


11 


IS 


33 


J 


n 


n 


29 


26 


3038 


23 


34 


40 


ZO 


38 


32 


29 


13 


35 


25 


18 


37 


27 


42 


14 


31 


24 


16 


36 


33 


27 


11 


17 


33 


32 


38 


23  35 


25 


28 


36 


13 


39 


36 


26 


30 


22 


\\ 


13 


27 


a) 


33 


33 


32 


5  42 


40 


C  34 


23 


36 


3G 


37 


32 


28 


22 


20 


10 


40 


23 


16 


26 


30 


23 


41 


35 


37 


39 


17 


25 


13 


14 


34 


42 


33 


2     4   6     8    10  /2  14  /6  /a  ZO  ZZ  14  26  ZB  JO  3Z  34  36  38  40  4Z  44 
P/o  t    AV/?7  ber*s 

Fitf.  l.'i.—  Diagram  of  experimental  field  showing  location  of  the  respective 
treatments   by   number. 


Bui*.  451]        fertilizer  trials  in  a  bearing  citrus  grove 


37 


In  case  differences  in  relative  production  of  various  plots  which  have 
been  observed  to  date  do  not  prove  to  be  maintained  in  the  future,  it 
may  still  be  feasible  to  draw  conclusions  as  to  the  effect  of  the  treat- 
ments by  taking  into  account  the  trend  of  changes  in  relative  pro- 
ductivity in  various  sections  of  the  field  as  indicated  by  the  25  'con- 
tinuity' plots,  and  by  the  use  of  standardized  methods  of  measuring 
the  significance  of  differences  between  groups  of  plots. 

The  location  in  the  field  of  each  treatment  is  shown  in  figure  13. 
In  this  illustration  the  various  plots  are  designated,  first,  by  the 
letter  of  the  block  in  which  they  occur,  and,  second  by  the  number  of 
the  plot  in  the  particular  block.  The  letters  designating  the  blocks 
are  shown  on  the  left  margin,  and  plot  numbers  in  each  block  are 
shown  along  the  top  and  bottom  margins  of  the  diagram.  The  treat- 
ments assigned  to  each  plot  are  indicated  by  numerals  placed  in  each 
respective  plot  space.  The  treatment  which  each  plot  receives  may  be 
found  by  reference  to  table  12,  which  also  contains  a  list  of  all  plots 
receiving  a  given  treatment. 


TABLE  12 

List   and   Location   of    Treatments   with   Amounts    of   Certain    Fertilizer 

Ingredients  Applied  During  the  Early  Years  of  the  Experiment 

(Four  plots  per  treatment  unless  otherwise  stated) 


Materials  and  treatment 

Pounds  of  nitrogen  (N), 

phosphoric  acid  (P2O.,), 

potash  (K2O),  applied 

per  tree  per  year  from 

each  material 

Location  in  field 

"C"    (25  plots) 

Ammonium  nitrate 

0.33  N 
0.17N 

0.50  N 

D  8         F36        H48         K20 

Blood 

D24         P'52          I  4        K44 

Manure 

D38        G24        I  28         L10 

D48        G44          J  8         L30 

1.   No  treatment 

E  4        H16          .734        M  4 

E20        H36         K  6        M24 

M40 

D18        G38         J38         L14 

2.   Ammonium  nitrate 

No  cover  crop 

ION 

D22         F38          J40        M  6 

3.  Ammonium  nitrate 

Triple  superphosphate 

ION 
1  0  P2Ot 

D28        G40         K40         L16 

4.   Ammonium  nitrate 

Triple  superphosphate 

ION 

10  p2o5 

1.0  KsO 

D26        G42         K38        M16 

No  cover  crop 

5.   Ammonium  nitrate 

ION 
1  0  K2O 

E22         F42         K32        M14 

Sulphate  of  potash 

No  cover  crop 

6.   Cover  crop  alone  (6  plots) 

ION 

D12        H32         J  4         L22 

7.   Ammonium  nitrate 

E  6        H34         J12         1-28 

Cover  crop 

38 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Table  12 — (Continued) 


Materials  and  treatment 


8.  Ammonium  nitrate 

Triple  superphosphate 

Cover  crop 

9.  Ammonium  nitrate 

Triple  superphosphate 

Sulphate  of  potash 

Cover  crop 

10.  Ammonium  nitrate 

Triple  superphosphate 

Muriate  of  potash 

Cover  crop 

11.  Ammonium  nitrate 

Sulphate  of  potash 

Cover  crop 

12.  Ammonium  sulfate 

Nitrate  of  soda 

Blood 

Cover  crop 

13.  Ammonium  sulfate 

Nitrate  of  soda 

Blood 

Phosphate 

Sulphate  of  potash 

Cover  crop 

14.  Ammonium  nitrate 

Blood 

Manure 

Phosphate 

Muriate  of  potash 

Cover  crop 

15.  Ammonium  sulfate 

Cover  crop 

16.  Ammonium  sulfate 

Limestone 

Cover  crop 

17.  Blood 

Cover  crop 

18.  Urea 

Cover  crop 

19.  Ammonium  nitrate 

Blood 

Cover  crop 

20.  Nitrate  of  lime 

No  cover  crop 

21.  Nitrate  of  lime  in  February 

Cover  crop 

22.  Nitrate  of  lime  in  June 

Cover  crop 

23.  Nitrate  of  lime  in  October 

Cover  crop 

24.  Nitrate  of  lime  in  three  applications 
Cover  crop 

25.  Nitrate  of  lime 

Nitrate  of  soda 

Cover  crop 

26.  Nitrate  of  soda 

No  cover  crop 


Pounds  of  nitrogen  (N) , 

phosphoric  acid  (P2OO, 

potash  (K2O) ,  applied 

per  tree  per  year  from 

each  material 


1.0N 
I.OP2O5 

ION 
I.OP2O5 
1.0  K2O 

ION 
I.OP2O5 
1.0  K2O 

ION 
1.0  K2O 

0.33  N 
0.33  N 
0.33  N 

0.33  N 
0.33  N 
0.33  N 
1.25  P2O5 
0.66  K2O 

0.33  N 
0.17N 
0.50  N 
IOP2O5 
1.0  K2O 


ION 

ION 

1.0N 

ION 

0.67N 
0.33  N 

ION 

ION 

ION 

ION 

ION 

0  50  N 
0.50  N 

ION 

Location  in  field 


E12  H46  J18  L20 

E14  I  42  J10  L18 

E  2  H40  J14  L26 

E16  H42  J22  L32 

D  2  G48  I  12  M28 

D  6  G50  I  10  M26 

E  8  H50  J16  M30 


D46  I  18  K30  M18 

H20  J28  K42  M  2 

F46  I  34  K22  M22 

F50  I  6  K28  M12 

F32  I  22  K10  M20 

E18  F40  J32  L  6 

D32  H24  I  40  LI 2 

F48  H22  J30  M38 

D42  H26  J42  L  2 

D44  G32  I  24  K18 

D54  G46  I  26  K12 

D50  H30  J  2  L42 


Eul.  451 


FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


39 


Table  12—  (Concluded) 


Materials  and  treatment 


27. 


28. 


30. 


31 


32. 


33. 


Nitrate  of  soda 

Cover  crop 

Nitrate  of  soda 

Gypsum 

Cover  crop 

29.  Nitrate  of  soda 

Manure 

Cover  crop 

Manure  broadcast  in  fall 

No  cover  crop 

Manure  broadcast  in  fall 

Cover  crop 

Manure  broadcast  in  spring 

Cover  crop 

Manure  in  furrows  in  fall 

Cover  crop 

34.  Ammonium  nitrate 

Blood 

Manure 

Gypsum 

Cover  crop 

35.  Ammonium  nitrate 

Blood 

Manure 

Limestone 

Cover  crop 

Alfalfa  hay  on  nitrogen  basis 

Ammonium  nitrate 

Blood 

Cover  crop 

Bean  straw  on  nitrogen  basis 

Ammonium  nitrate 

Blood 

Cover  crop 

Wheat  straw  on  nitrogen  basis 

Ammonium  nitrate 

Blood 

Cover  crop 

39.  Wheat  straw  on  organic  matter  basis 

Ammonium  nitrate 

Blood 

Cover  crop 

40.  Amount  halved 

Ammonium  nitrate 

Blood 

Manure 

Cover  crop 

Amount  doubled 

Ammonium  nitrate 

Blood 

Manure 

Cover  crop 

Amount  trebled 

Ammonium  nitrate 

Blood 

Manure 

Cover  crop 


36 


37 


38. 


41 


42. 


Pounds  of  nitrogen  (N), 

phosphoric  acid  (P2O5), 

potash  (K2O),  applied 

per  tree  per  year  from 

each  material 


ION 


ION 

0  50  N 
0.50  N 

ION 

1.0N 

ION 

ION 

0.33  N 
0.17N 
0.50  N 

0.33  N 
0.17N 
0.50  N 

0  50  N 
0.33  N 
0.17N 

0.50  N 
0.33  N 
0.17N 

0.50  N 
0.33  N 
0.17N 

0.13*N 
0.58  N 
0.29  N 

0  17N 

0.08  N 
0.25  N 

0.67N 
0  33  N 
ION 

1.00  N 

0  50  N 

1  50  N 

Location  in  field 


D52  G22  I  32 

D40  H18  J26 

F44  I  2  K36 

D30  I  30  K  2 

D20  I  36  K16 

G34  I  38  K24 

F34  H54  J20 

D36  H52  J36 

D10  H28  J44 

G30  I  20  K26 

D34  H38  I  14 


G26 


K  4 


G28        H14  J24 


D  4        G36         J  6 


E10        G52        I  44 


E24        G54        I  16 


K14 
L38 

M  8 

M42 
M34 
L  8 
M32 
L  4 

M10 

M36 
L44 
L36 
M44 

L40 

K  8 
K34 


*  Based  on  analysis  of  material  applied  spring  of  1927. 


40  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


DIFFERENTIAL    FERTILIZER    AND    CULTURAL    TREATMENTS 

The  gradual  increase  in  the  knowledge  of  the  culture  and  nutri- 
tion of  citrus  fruits  has  raised  a  large  number  of  questions  for  solu- 
tion which  may  properly  be  included  among  the  trials  under  con- 
sideration. However,  the  purposes  of  these  trials  are  not  confined  to 
the  determination  of  the  effect  of  specific  treatments  on  the  produc- 
tion of  oranges  alone.  It  is  expected  that  the  effect  of  many  of  the 
fertilizer  treatments  may  cause  such  ultimate  differences  in  the  soil 
conditions,  that  valuable  material  will  be  produced  for  future  labora- 
tory studies  upon  the  fundamental  processes  which  may  be  involved. 
The  effect  of  some  of  the  treatments  may  not  be  apparent  during  the 
early  progress  of  the  trials,  but  the  continued  application  of  these 
materials  may  have  a  gradual  effect  upon  both  the  trees  and  the 
soil9  which  may  be  cumulative  with  the  passing  of  time. 

The  great  diversity  and  the  seeming  importance  of  the  problems 
which  have  been  raised  have  prompted  an  effort  to  secure  suggestions 
from  many  sources.  On  August  28,  1926,  a  general  meeting  was 
called  for  this  purpose  at  the  Citrus  Experiment  Station  by  the 
Director.  Citrus  growers,  members  of  the  Staff  of  the  College  of 
Agriculture  and  those  interested  in  the  sale  of  fertilizer  materials, 
have  all  contributed  to  the  plans  finally  adopted.  Frequent  con- 
ferences have  been  held  informally  with  these  persons. 


9  In  order  that  adequate  material  may  be  supplied  for  laboratory  studies 
upon  the  source  of  changes  which  may  be  produced  in  the  soil  after  various 
treatments,  the  soil  of  this  orchard  has  been  thoroughly  sampled,  once  during 
the  winter  of  1918-19,  and  again  at  the  time  the  differential  treatments  com- 
menced in  February,  1927.  These  samples  are  now  in  storage.  It  is  planned 
that  soil  samples  will  be  taken  at  periodic  intervals  throughout  the  duration 
of  the  experiments  for  use  in  laboratory  studies.  Although  the  materials  which 
will  be  applied  will  be  as  pure  as  it  is  practicable  to  purchase  commercially, 
it  is  also  planned  that  samples  of  them  will  be  taken  for  future  study.  Hence, 
it  may  be  possible  to  determine  whether  or  not  the  effects  of  the  treatment 
are  actually  due  to  the  material  being  consciously  tested,  or  to  the  effects  of 
impurities  in  it.  The  arrangement  of  the  experimental  field  and  the  nature  of 
the  trials  which  are  described  are  the  results  of  the  combined  efforts  of  a 
large  number  of  people.  In  connection  with  the  planning  of  the  treatments 
suggestions  have  been  sought  from  many  sources.  The  advice  of  many  mem- 
bers of  the  staff  of  the  Citrus  Experiment  Station  lias  been  of  great  influence 
in  determining  the  nature  of  the  trials  to  be  made.  Among  these  men  are 
H.  J.  Webber,  A.  R.  C.  Haas,  W.  P.  Kelley,  W.  R.  Schoonover,  J.  Gordon  Surr, 
and  R.  S.  Vaile.  The  successful  supervision  of  the  field  work,  which  is  essen- 
tial to  an  experiment  of  this  kind,  has  been  due  at  various  times  to  the  efforts 
of  W.  M.  Mertz,  J.  A.  Prizer,  and  Charles  Wilson. 


BuL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  41 

The  trials  indicated  in  table  12  have  been  selected  as  incorporating 
the  most  essential  ideas  involved  in  the  suggestions  which  have  been 
made.  The  elimination  of  many  trials  which  possibly  would  have 
contributed  much  valuable  information  was  necessitated  by  the 
physical  limitations  of  the  experimental  field. 

As  heretofore  stated,  each  of  the  42  treatments  is  repeated  four 
times.  These  repetitions  are  distributed  on  the  basis  which  has  been 
discussed  in  the  previous  section  of  this  paper.  The  location  of  each 
in  the  field  is  shown  in  table  12.  In  general  the  amounts  of  the  ele- 
ments or  materials  applied  are  in  harmony  with  conservative  com- 
mercial practice.  During  the  early  years  of  the  trials  it  is  expected 
that,  unless  otherwise  stated,  one  pound  of  actual  nitrogen  (N), 
phosphoric  acid  (P205),  and  potash  (K20),  respectively,  will  be 
applied  per  tree  each  year,  in  each  instance  where  these  materials  are 
used.  This  general  rule  is  to  be  followed  regardless  of  the  material 
by  which  they  are  supplied.  Gypsum  and  limestone  are  to  be  used 
at  the  rate  of  one  ton  per  acre  per  year,  the  gypsum  to  be  supplied 
annually  and  the  limestone  every  four  years.  The  concentrated  fer- 
tilizers are  to  be  applied  in  the  early  spring  unless  otherwise  stated. 
The  bulky  organic  materials  are  to  be  applied  in  the  late  summer  or 
early  fall  with  the  exception  of  one  treatment. 

Any  discussion  or  grouping  of  the  treatments  on  the  basis  of  their 
experimental  purposes  involves  some  duplication  and  perhaps  some 
confusion.  Many  comparisons  may  be  made  between  a  single  trial 
and  several  other  trials,  not  all  of  which  can  be  placed  in  a  simple  out- 
line of  comparison.  In  indicating  the  general  scope  and  some  of  the 
chief  divisions  of  the  experiments,  however,  it  may  be  well  to  call 
attention  to  the  treatments  which  most  obviously  fall  under  each 
division. 

The  more  general  groups  of  treatments  to  be  employed  follow. 
Experimental  trials  are  referred  to  by  number,  the  exact  treatment 
of  which  may  be  obtained  from  table  12. 

A.  As  heretofore  noted,  25  plots,  designated  as  'C  plots,  have 
been  distributed  throughout  the  field  to  indicate  the  degree  of  the 
continuity  of  differences  of  normal  yield  of  various  parts  of  the  field. 
These  plots  will  serve  as  indices  of  relative  fertility  and  will  be  an 
aid  in  the  interpretation  of  all  results.  The  standard  amount  of  one 
pound  of  nitrogen  per  tree  is  to  be  applied  annually  during  the  first 
few  years  of  the  experiment.  One-half  the  nitrogen  is  to  be  in  the 
form  of  concentrated  materials  applied  in  the  spring,  and  one-half  as 
bulky  organic  material  applied  in  the  fall.     The  concentrated  mate- 


42  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

rials  will  consist  of  ammonium  nitrate,  which  will  supply  %  pound 
of  nitrogen,  and  dried  blood,  which  will  supply  %  pound  of  nitrogen. 
The  bulky  organic  material  will  be  dairy  manure,  and  will  supply 
one-half  the  total  nitrogen  applied.  Winter  cover  crops  will  also 
be  grown  on  all  C  plots. 

B.  A  series  of  trials  have  been  installed  to  determine  the  effects 
of  nitrogen,  phosphoric  acid,  and  potash,  with  and  without  a  cover 
crop.     This  group  of  treatments  may  be  subdivided  as  follows: 

I.  Ten  treatments  involve  essentially  the  use  of  ammonium  nitrate 
(N),  triple  superphosphate  (P),  sulphate  of  potash  (K),  and  cover 
crop.  The  materials  are  applied  in  standard  quantities  alone  and 
in  the  following  combinations: 


Clean 

culture 

Cover 

crop 

No. 

No. 
6. 
7. 

2.       N 





N 





3.       N 

P 

— 

8. 

N 

P 

— 

4.        N 

P 

K 

9. 

N 

P 

K 

5.       N 

— 

K 

11. 

N 

— 

K 

II.  One  treatment  (No.  10)  substitutes  muriate  of  potash  in  treat- 
ment 9  above  to  determine  the  possible  effect  of  accumulations  of 
chlorin  as  compared  with  the  sulfate  radicle  in  the  presence  of 
nitrogen  and  phosphoric  acid. 

III.  Two  trials  (Nos.  12  and  13)  were  inaugurated  to  determine 
the  value  of  phosphoric  acid  and  potash  in  the  presence  of  several 
nitrogen-carrying  fertilizers  combined.  The  standard  amount  of 
actual  nitrogen,  one  pound  per  tree,  has  been  used,  but  the  approxi- 
mate proportions  of  the  materials  used  to  supply  it,  and  also  the 
amounts  of  phosphoric  acid  and  potash  used,  have  been  determined 
by  averaging  the  four  most  popular  so-called  'complete  commercial 
fertilizers'  used  at  the  present  in  citrus  orchards.  This  average  gave 
fertilizers  of  the  order  of  7.5  per  cent  N,  9.25  per  cent  P205,  4.75  per 
cent  K20.  When  all  fillers  are  eliminated  this  becomes  9.7  :11.9  :6.15, 
which  is  the  formula  employed.  The  materials  used  are  ammon- 
ium sulfate,  nitrate  of  soda,  and  blood  (each  supplying  one-third  of 
the  total  nitrogen),  triple-superphosphate  and  sulfate  of  potash.  The 
'complete  fertilizer'  has  been  commercially  mixed.  These  two  trials 
may  logically  be  compared  directly  with  several  others  in  this  series, 
as  a  study  of  table  12  will  show. 

IV.  One  trial  (No.  14)  deals  with  the  value  of  additions  of  phos- 
phoric acid  and  potash  in  the  presence  of  manure  when  the  latter  is 


BUL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  4.'} 

supplied  in  such  an  amount  that  it  provides  one-half  the  total  quantity 
of  nitrogen  applied. 

V.  The  necessity  of  nitrogenous  fertilization  in  the  culture  of 
citrus  fruits  in  California  has  stimulated  the  adoption  of  an  extensive 
series  of  trials  of  nitrogen-carrying  materials  (Nos.  2,  7,  15,  16,  17,  18, 
19,  20,  21,  26,  27,  28,  29,  30,  31).  These  have  been  chosen  in  an 
effort  to  determine  the  efficiency  of  various  substances  supplying  equal 
amounts  of  total  nitrogen.  The  results  of  continued  applications  of 
various  chemical  constituents  associated  with  the  carriers,  and  the 
interrelations  of  several  of  these  constituents  will  also  be  the  subject 
of  study.  The  effect  of  the  so-called  'soil  amendments'  may  also  be 
considered  in  this  section,  since  they  contain  chemical  constituents 
which  may  react  with  the  fertilizer  material.  Clean  culture  and  cover 
cropping  will  be  employed  in  special  instances  in  an  attempt  to  deter- 
mine the  effect  of  organic  matter  on  the  soil  reactions  to  various 
fertilizer  materials  as  well  as  on  tree  growth. 

VI.  The  effect  of  supplying  nitrogenous  material  at  various  seasons 
will  be  studied  (Nos.  21,  22,  23,  24,  31,  32).  These  materials  will 
consist  of  nitrate  of  lime  and  dairy  manure,  respectively,  each  to 
supply  the  standard  amount  of  nitrogen.  The  nitrate  of  lime  will 
provide  nitrogen  in  an  available  form  and  will  give  some  information 
as  to  the  time  at  which  citrus  trees  require  this  material  for  best 
response.  The  manure  will  serve  for  the  study  of  the  reaction  of  the 
tree  and  soil  to  organic  and  slowly  available  nitrogenous  materials 
when  applied  at  different  seasons. 

VII.  The  method  of  applying  bulky  organic  materials  (Nos.  31, 
32,  33)  is  the  subject  of  a  trial  comparing  the  application  of  dairy 
manure  by  means  of  broadcasting  and  in  furrows. 

VIII.  Four  trials  (Nos.  16,  28,  34,  and  35),  are  being  made  to 
determine  the  effects  of  soil  amendments  under  various  conditions  of 
culture. 

IX.  The  effect  of  the  addition  of  various  bulky  organic  materials 
is  to  be  studied  in  an  effort  to  determine  the  specific  effect  of  such 
materials,  the  desirable  amount  of  organic  matter  to  apply,  and  also 
the  value  of  materials  low  in  nitrogen.  In  certain  trials  the  organic 
materials  will  be  applied  in  such  a  quantity  that  they  will  supply 
half  the  total  nitrogen  (Nos.  36,  37,  38,  and  C).  The  amount  of 
organic  matter  will  therefore  vary  in  quantity  with  the  materials 
used.  In  another  trial  (No.  39)  the  bulky  materials  will  be  applied 
in  such  amounts  that  the  organic  matter  to  be  added  in  the  form  of 


44  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

wheat  straw  will  be  equal  to  that  contained  in  dairy  manure  when 
the  latter  material  supplies  half  the  total  nitrogen.  In  all  cases  the 
total  nitrogen  applied  will  be  made  up  to  the  standard  amounts  with 
ammonium  nitrate  and  dried  blood. 

X.  The  effect  upon  trees  and  soil  of  supplying  various  total 
amounts  of  nitrogen  will  be  investigated  in  certain  trials  (Nos.  40,  41, 
42,  and  C).  These  experiments  will  serve  as  a  guide  in  determining 
the  standard  amount  of  this  element  to  be  applied  in  the  future  years 
on  this  experimental  field.  They  may  also  give  some  information  as  to 
the  most  economical  use  of  nitrogenous  fertilizers  on  Ramona  loam 
and  on  similar  soil  types.  The  nitrogen  in  this  series  of  trials  is  to  be 
derived  from  concentrated  and  bulky  material  as  follows :  two-sixths 
of  the  total  amount  to  be  supplied  by  ammonium  nitrate,  one-sixth  by 
dried  blood,  and  three-sixths  by  dairy  manure. 


APPENDIX 

COST    OF    DEVELOPING    AND    MAINTAINING    THE    EXPEEIMENTAL 
GEOVE  DUEING   THE   FIEST   TEN-YEAE  PEEIOD 

A  record  has  been  kept  of  the  expenses  incurred  in  the  develop- 
ment of  the  experimental  orchard.  Several  of  the  ordinary  items  of 
expense  which  must  be  met  by  the  commercial  grower  have  naturally 
not  been  among  the  necessary  charges  met  by  a  state  institution. 
Among  such  charges  are  taxes,  interest  on  investment  and,  in  this 
particular  instance,  the  usual  expense  of  water  rights,  which  may 
normally  be  charged  against  such  an  enterprise.  The  actual  cost  of 
the  development  as  experienced  can  not,  therefore,  be  used  as  an 
absolute  criterion  of  the  expense  which  may  be  anticipated  in  connec- 
tion with  the  establishment  of  a  commercial  orchard.  It  may,  how- 
ever, be  interesting  to  present  the  record  of  the  actual  cost  of  develop- 
ment plus  the  ordinary  average  charges  which  would  have  been  made 
against  such  a  property  were  it  owned  and  financed  by  a  private 
commercial  organization. 

The  actual  ten-year  expenditure  for  development  by  the  Experi- 
ment Station,  including  original  capital  investment  less  the  assumed 
charge  of  $200  an  acre  for  water,  plus  material  and  labor  equals 
$1,508.26  an  acre.  During  the  same  period  the  sale  of  the  bean  inter- 
crops plus  the  sale  of  the  fruit  totaled  $1,653.13.  The  orchard  has 
thus  repaid  all  capital  expenditure  and  costs  of  operation,  and  shows 
a  balance  of  $144.87  an  acre  to  the  Experiment  Station  at  the  end  of 
the  first  ten-year  period. 


Bul.  451 


FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


45 


TABLE  13 

Summary  of  Accumulated  Cost  Per  Acre  of  Developing  Orange  and 

Grapefruit  Orchard 

(Includes  charges  for  supervision,  taxes,  depreciation  and  interest. 

Sales  are  credited.) 


Material 
and 
labor 

Supervi- 
sion and 
miscel- 
laneous 
labor 

Taxes* 

Inter- 
est*! at 
6% 

Total 
charges 

Sales 
total  net 
returns 

Net 
debit 

Net 
credit 

Total 
accumu- 
lated 
invest- 
ment 

Original  capital 

investment 

$676,101: 

$  676.10 

July  I,  1917,  to 

June  30,  1918.. 

45.63 

$37.46 

$  5.00 

$40.57 

$128.66 

$  46  19$ 

$  82.47 

758.57 

July  1,  1918,  to 

June  30, 1919... 

51  75 

37.46 

5.00 

45  51 

139.72 

25.16§ 

114.56 

873.13 

July  1,  1919,  to 

June  30, 1920. . 

69.23 

37.46 

5  00 

52.39 

164.08 

54  08§ 

110.00 

983.13 

July  1,  1920,  to 

Dec.  31,  1920. 

22.54 

18.73 

2.50 

29.49 

73.26 

46.23§ 

27.03 

1010  16 

Jan.  1,  1921,  to 

Dec.  31,  1921.. 

99.30H 

37.46  ! 

7.00 

60.61 

204.37 

56.481 

147.89 

1158  05 

Jan.  1,  1922,  to 

Dec.  31,  1922... 

86.79 

37  46j 

7.00 

69.48 

200.73 

184.771 

15.96 

1174  01 

Jan.  1,  1923,  to 

Dec.  31,  1923... 

291.60+ 

37.46 

11.00 

70  44 

410.50 

55.571 

354.93 

1528  94 

Jan.  1,  1924,  to 

Dec.  31,  1924. 

156.4411 

37  46 

11.00 

91.74 

296. 64* 

215.151 

81.49 

1610  43 

Jan.  1,  1925,  to 

Dec.  31,  1925... 

94.72 

37  46 

11  00 

96.63 

239. 81x 

495.911 

$256  10 

1354  33 

Jan.  1,  1926,  to 

Dec.  31,1926. 

114.1611 

37.46 

11.00 

81.26 

.  243. 88x 

473.591 

229.71 

1124.62 

*  Charges  made  but  not  actually  paid. 

t  Interest  is  charged  on  total  accumulated  investment  existing  at  end  of  previous  fiscal  period,  but 
not  on  operating  charges  or  surplus  of  the  current  period. 
%  Includes  charges  as  follows 

Cost  of  land $300.00 

Average  cost  of  water 200.00 

Pipe  lines,  installed 91.40 

Preparing  land 10.00 

Digging  holes 2.70 

Balling  trees 4  50 

Trees,  90  at  75  cents 67.50 

Total $676.10 

§  Receipts  from  sale  of  beans. 

||  Includes  charges  for  fumigation. 

1  Receipts  from  sale  of  fruit. 

+  Includes  $202.64  for  orchard  heating  equipment 

x  Includes  depreciation  on  heating  equipment  at  5  per  cent  per  annum  ($10.13). 


46  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  figures  presented  in  table  13,  on  the  other  hand,  show  the 
normal  costs  of  developing  the  grove  if  such  charges  as  taxes,  water 
rights,  and  interest  on  capital  invested  were  charged  against  the 
undertaking.  The  figures  given  herein  may,  therefore,  be  used  by 
the  reader  as  a  basis  of  comparison  and  as  an  aid  in  estimating  the 
cost  of  establishing  a  commercial  grove.  It  will  also  be  our  endeavor 
to  show  where  the  charges  made  and  the  receipts  obtained  may  be 
in  any  way  uncommon,  in  order  that  the  records  may  not  be  mislead- 
ing if  taken  as  a  reasonable  estimate  of  such  costs.  The  actual  capital 
investment  per  acre  for  land,  a  theoretical  charge  for  water  rights,10 
the  cost  of  installation  of  pipe  lines,  and  that  of  planting  of  trees  are 
indicated  in  a  footnote  to  table  13. 

Although  pipe  lines  are  located  at  200-foot  intervals  and  the  cost 
of  this  item  is  greater  than  in  the  usual  planting,  the  costs  of  other 
items  are  rather  low.  The  price  of  the  land,  $300,  is  low  compared 
with  the  present  ruling  prices  being  paid  in  this  and  other  comparable 
orange-growing  districts.  The  cost  of  trees  is  somewhat  below  the 
average,  the  trees  were  all  grown  at  the  Experiment  Station. 

The  frost-protection  equipment  purchased  in  1923  and  charged 
in  table  13,  consists  partly  of  fifty  9-gallon  heaters  per  acre,  one  500- 
gallon  tank  wagon  to  each  8  acres,  sufficient  oil  storage  and  oil  to 
refill  all  of  the  heaters  four  times,  a  frost-alarm  system,  filling  buckets, 
and  torches.  The  initial  charge  for  this  equipment  was  $202.64  per 
acre.  Depreciation  has  been  charged  on  this  equipment  at  the  rate  of 
5  per  cent  per  annum. 

No  other  investment  charge  for  equipment  has  been  made  for  this 
particular  grove.  The  tools,  teams,  and  tractor  used  on  all  projects 
of  the  Experiment  Station  have  been  employed,  and  flat  charges  have 
been  made  against  this  acreage  according  to  the  services  rendered. 

The  cultivation  work  has  been  done  mainly  with  a  tractor.  The 
prevailing  rate  of  $2.50  an  hour  has  been  charged  for  all  tractor 
work.  The  rate  charged  for  team  work  has  been  $0.75  an  hour  for 
team  and  man.    Other  labor  has  been  charged  at  current  rates. 

The  charge  for  irrigation  water  has  approximated  very  closely  the 
average  which  would  have  been  experienced  had  actual  stock  in  the 
Gage  Canal  Company  been  held  by  this  property.  This  average  is 
$10.65  an  acre  annually  for  the  average  amount  used.    Nearly  all  the 

!<>  A  theoretical  charge  of  $200  per  acre  for  water  rights  is  included.  The 
grove  is  in  the  midst  of  a  large  acreage  of  citrus  served  by  the  Gage  Canal  Co. 
The  average  market  value  per  acre  of  stock  of  this  system  commonly  used  is 
therefore  used  as  the  theoretical  charge.  (See  Blaney,  Harry  F.  Cost  of 
water  to  irrigators  in  California.  California  State  Dept.  Public  Works,  Div. 
Eng.  and  Irrig.  Bui.  8:1-66.     1925.) 


BUD.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE  47 

fertilizer  which  has  been  used  has  been  the  legumes  grown  on  the 
land,  excepting  that  one-half  ton  of  alfalfa  straw  per  acre  was  pur- 
chased in  1924,  and  spread  in  the  irrigation  furrows  to  retard  the 
movement  of  irrigation  water  and  facilitate  its  penetration.  Certain 
cultural  costs  are  higher  than  would  occur  in  commercial  practice. 
Extra  care  has  been  taken  to  have  all  of  the  operations  done  as  uni- 
formly and  exactly  as  possible  over  the  entire  planting.  This  is 
particularly  true  of  irrigation.  Certain  charges  included  under  super- 
vision are  for  record  keeping.  These  charges  are  for  weighing  of 
beans  and  of  fruit,  measuring  the  top  volume  and  trunk  circumference 
of  the  trees,  etc. 

This  property  has  been  favored  with  comparative  freedom  from 
serious  tree  diseases.  Insect  pests  have  been  readily  kept  under  con- 
trol. Fumigation  has  been  necessary  only  three  times,  in  1921,  1924, 
and  1926. 

The  grove  has  returned  some  revenue  every  year  since  and  includ- 
ing the  year  it  was  planted.  The  returns  the  first  four  years  were 
from  the  sale  of  Black-eye  beans,  grown  on  the  land  as  an  intercrop. 
The  total  receipts  for  the  four  years  from  the  sale  of  beans  were 
$171.66  an  acre.  This  very  favorable  return  was  influenced  by  the 
fact  that  the  beans  were  grown  during  and  immediately  following  the 
period  of  the  World  War  when  especially  high  prices  were  received 
for  this  commodity.  In  spite  of  the  return  from  the  sale  of  beans 
during  the  first  four  years,  the  cultural  maintenance  charges  were 
such  that  the  capital  investment  had  increased  to  $1,010.16  an  acre  at 
the  time  when  the  trees  came  into  production. 

The  total  amount  received  from  the  sale  of  fruit  for  all  years  was 
$1,481.47  an  acre,  and  represents  the  value  of  six  crops  of  fruit  from 
the  grove,  from  its  fourth  year  to  and  including  its  ninth  year.  All 
of  the  fruit  has  been  sold  by  the  California  Fruit  Growers  Exchange. 
The  returns  over  the  six-year  period  include  the  usual  fluctuations  in 
prices. 

Table  13  indicates  the  capital  investment  under  the  heading 
"  Total  accumulated  investment"  at  the  close  of  each  fiscal  year  from 
the  time  of  planting  until  June  30,  1920,  and  for  each  calendar  year 
from  that  time  until  December  31,  1926.  It  may  be  observed  that  the 
first  year  in  which  an  actual  profit  occurred  was  1925,  at  which  time 
the  orchard  was  eight  years  old.  The  capital  investment  was  decreased 
both  that  and  the  following  year.  At  the  close  of  the  period  under 
discussion  the  total  investment  amounted  to  $1,124.62,  which  is  the 
net  cost  of  the  grove  per  acre  to  December  31,  1926.  An  evaluation 
of  the  grove  with  its  improvements  by  a  disinterested  professional 


48 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


appraiser  was  made  at  that  time.  A  conservative  estimate  of  $1,500 
per  acre  was  arrived  at.  It  was  stated  that  this  amount  should  be 
realized  if  the  property  were  disposed  of  at  a  forced  sale.  The  differ- 
ence between  this  figure  and  the  total  accumulated  cost  represents  the 
theoretical  profit  from  the  undertaking  from  a  commercial  point  of 
view.  This  figure  amounts  to  $375.38  per  acre,  or  $18,037.01  for  the 
entire  tract  of  48.05  acres. 


TABLE  14 

Net   Beturns*   for  Varieties   per   Pound,    1921-1926,   Inclusive 


Variety  or  kind 

1921 

1922 

1923 

1924 

1925 

1926 

Average 

Navels 

Valencias 

Grapefruit 

$0.02125 
.02162 
.01981 

$0.04810 
.03349 
.04261 

$0.02125 
.01311 
— .00649 t 

$0.01092 
.02403 
.01653 

$0.04212 

.05962 
.03498 

$0  03228 
.03423 
.03166 

$0.02932 
.03107 
.02318 

*  Net  to  grower. 

t  Packing,  selling,  and  transportation  charges  exceeded  the  gross  returns  by  this  amount. 

The  net  prices  received  per  pound  for  each  variety  of  citrus — 
Valencia  and  Navel  oranges  and  Marsh  Seedless  grapefruit — each 
year,  are  noted  in  table  14.  In  general  they  are  typical  of  average 
prices  paid  during  these  years,  and  are  influenced  by  the  usual  factors 
affecting  supply  and  demand.  The  value  per  pound  of  all  marketable 
fruit  was  increased  in  1922  by  the  occurrence  of  a  freeze  which  cut 
down  the  total  amount  of  fruit  shipped.  This  freeze  did  not,  however, 
affect  the  accuracy  of  the  yield  records  of  Navel  oranges.  Heaters 
were  installed  in  1923,  and  no  further  loss  has  been  experienced  from 
this  source.  Although  the  average  price  has  been  satisfactory,  the 
returns  per  pound  from  the  sale  of  grapefruit  have  been  more  variable 
than  from  the  sale  of  the  two  varieties  of  oranges. 

As  a  basis  of  comparison  of  the  returns  from  the  three  varieties 
of  fruit,  their  production  has  been  calculated  as  if  they  were  in  a 
solid  planting.  The  average  yield  of  a  solid  acre  of  each  variety  is 
noted  in  table  15  for  each  of  the  six  years  under  discussion,  as  well 
as  the  total  for  this  period.  The  heavier  production  of  grapefruit  is 
notable.  The  total  production  of  Navels  and  Valencias  is  about  equal, 
but  it  is  apparent  that  certain  years  have  been  more  favorable  for 
the  production  of  one  variety  than  for  the  other  in  this  particular 
orchard  under  conditions  of  uniform  care.  In  1922,  for  example,  the 
damage  from  frost  was  not  so  severe  in  the  cases  of  the  Valencias  and 
the  grapefruit  as  in  the  case  of  the  Navels.  The  yield  of  Navels  was 
markedly  higher  than  that  of  Valencias  in  1925  for  some  reason  which 
has  not  been  ascertained. 


BUL.  451]  FERTILIZER    TRIALS    IN    A    BEARING    CITRUS    GROVE 


49 


The  total  gross  return  from  all  three  varieties  has  been  calculated 
on  the  acre  basis  and  appears  in  table  16.  Over  the  six-year  period 
Valencias  and  grapefruit  have  netted  about  an  equal  amount  and  have 
been  slightly  more  profitable  than  Navels.  The  greater  return  from 
grapefruit  during  1921  and  1922  is  a  noticeable  feature  of  this  table, 
although  an  actual  loss  occurred  with  this  crop  in  1923. 


TABLE  15 

Yield  of  Varieties  on  an  Acre  Basis, 

(Pounds) 


1921-1926,  Inclusive 


Variety  or  kind 

1921 

1922 

1923 

1924 

1925 

1926 

Total 

Navels 

Valencias 

Grapefruit 

l,945f 

1,948 

4,535 

2,669* 

5,330 

6,125 

6,168f 

5,855 

9,160 

ll,924f 

10,649 

16,881 

13, 085 f 
8,227 
12,377 

10,678f 

15,999 

17,606 

46,469 
48.008 
66,684 

*  Based  on  an  area  of  18.29  acres  of  Navels,  14.99  acres  of  Valencias,  and  14.77  acres  of  grapefruit; 
total  area,  48.05  acres. 

t  Navel  yields  in  this  table  are  somewhat  lower  than  those  in  table  6,  the  latter  includes  windfalls, 
whereas  this  table  records  only  fruit  which  went  to  packing  house. 

|  This  is  only  37  per  cent  of  total  production,  remainder  not  sold  on  account  of  frost  injury. 


TABLE  16 
Gross  Returns*  for  each  Variety  per  Solid  Acre,  1921-1926,  Inclusive 


Variety  or  kind 

1921 

1922 

1923 

1924 

1925 

1926 

Total 

Navels 

Valencias 

Grapefruit 

$41.33 
42.11 
89.82 

$128.37 
178.50 
260.98 

$131  07 

76.76 

—59.45 

$130.21 
255.90 
279.04 

$551  14 

490.49 
432.95 

$344.69 
547  54 
557.40 

41,326.81 
1.591  30 

1,560.74 

Charges  for  picking  and  hauling  have  been  deducted 


The  reader  should  not  use  tables  13,  15,  and  16  as  an  indication  of 
the  returns  which  may  be  reasonably  expected  from  a  commercial 
grove  without  being  fully  aware  that  the  average  prices  set  forth  in 
table  14  from  1921  to  1926,  inclusive,  are  considerably  above  the  ten- 
year  average  of  1912-22.  Furthermore  the  average  price  received 
from  the  sale  of  oranges  for  the  years  1925  and  1926,  3.7  cents  a  pound 
for  Navels  and  4.7  cents  a  pound  for  Valencias,  is  approximately 
double  the  average  return  for  the  ten-year  period  1912-22. 1X  It  was 
during  these  two  years  of  high  prices  that  two  out  of  the  three  really 
commercial  yields  were  obtained  from  this  orchard.  The  total  returns 
have,  therefore,  been  considerably  higher  than  can  be  expected  on 
the  average  from  similar  orchards. 


11  Vaile,   K.    S.      A   survey   of   orchard   practices    in    the    citrus   industry    of 
southern  California.     California  Agr.  Exp.  Sta.  Bui.  374:1-40.     1924. 


STATION  PUBLICATIONS  AVAILABLE  FOE  FREE  DISTRIBUTION 


BULLETINS 
No. 


No. 

253.  Irrigation  and   Soil  Conditions  in  the  386. 

Sierra   Nevada   Foothills,    California. 

262.  Citrus   Diseases  of   Florida   and   Cuba  387. 

Compared  with  those  of   California.  388. 

263.  Size  Grades  for  Ripe  Olives. 

268.  Growing  and  Grafting  Olive  Seedlings  389. 

273.   Preliminary  Report  on  Kearney  Vine-  390. 

yard     Experimental     Drain,     Fresno 
County,    Calif.  391. 

277.  Sudan  Grass. 

278.  Grain  Sorghums.  392. 

279.  Irrigation  of  Rice  in  California.  393. 
283.  The  Olive  Insects  of  California.  394. 
304.  A  Study  of  the  Effects  of  Freezes  on 

Citrus  in  California. 

310.  Plum  Pollination.  395. 

313.  Pruning      Young      Deciduous      Fruit 

Trees.  396. 

324.   Storage  of  Perishable  Fruits  at  Freez- 
ing Temperatures.  397. 

328.   Prune   Growing  in   California. 

331.   Phylloxera-resistant  Stocks.  398. 

335.  Cocoanut  Meal   as  a   Feed  for   Dairy  400. 

Cows  and  Other  Livestock.  402. 

340.   Control     of     the     Pocket     Gopher     in  404. 

California.  405. 

343.  Cheese   Pests  and  Their  Control.  406. 

344.  Cold   Storage   as   an   Aid   to   the   Mar-  407. 

keting  of  Plums,  a  Progress  Report. 

347.  The  Control  of  Red  Spiders  in  Decid- 

uous Orchards.  408. 

348.  Pruning  Young  Olive  Trees.  409. 

349.  A    Study    of    Sidedraft    and    Tractor 

Hitches. 

350.  Agriculture     in     Cut-Over     Redwood 

Lands.  410. 

353.  Bovine    Infectious   Abortion,    and   As- 

sociated Diseases  of  Cattle  and  New- 
born Calves.  411. 

354.  Results  of  Rice  Experiments  in  1922. 

357.  A    Self-Mixing    Dusting    Machine    for  412. 

Applying  Dry  Insecticides  and  Fun- 
gicides. 

358.  Black    Measles,    Water    Berries,     and  414. 

Related  Vine  Troubles. 

361.  Preliminary  Yield  Tables  for   Second-  415. 

Growth   Redwood.  416. 

362.  Dust  and  the  Tractor  Engine. 

363.  The  Pruning  of  Citrus  Trees  in  Cali-  417. 

fovnia. 

364.  Fungicidal    Dusts   for   the    Control    of  418. 

Bunt. 

366.  Turkish     Tobacco     Culture,     Curing,  419. 

and  Marketing. 

367.  Methods  of  Harvesting  and  Irrigation  420. 

in  Relation  to  Moldy  Walnuts. 

368.  Bacterial      Decomposition     of      Olives  421. 

During  Pickling.  422. 

369.  Comparison     of     Woods     for     Butter 

Boxes.  423. 

370.  Factors    Influencing   the    Development 

of  Internal  Browning  of  the  Yellow  424. 

Newton  Apple. 

371.  The   Relative   Cost   of   Yarding    Small  425. 

and  Large  Timber.  426. 

373.  Pear   Pollination. 

374.  A    Survey    of    Orchard    Practices    in  427. 

the     Citrus     Industry     of     Southern 
California.  428. 

375.  Results   of   Rice   Experiments   at   Cor- 

tena,   1923,  and  Progress  in  Experi- 
ments in  Water  Grass  Control  at  the  429. 
Biggs  Rice  Field   Station,    1922-23.  430. 
377.  The  Cold  Storage  of  Pears.  431. 

379.  Walnut  Culture  in   California. 

380.  Growth    of    Eucalyptus    in    California  432. 

Plantations. 
382.   Pumping    for    Draininge    in    the    San  433. 

Joaquin   Valley,    California. 
385.   Pollination  of  the  Sweet  Cherry. 


Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig   Smut. 

The  Principles  and  Practice  of  Sun- 
Drying  Fruit. 

Berseem  or  Egyptian  Clover. 

Harvesting  and  Packing  Grapes  in 
California. 

Machines  for  Coating  Seed  Wheat 
with   Copper   Carbonate   Dust. 

Fruit  Juice  Concentrates. 

Crop   Sequences  at  Davis. 

I.  Cereal  Hay  Production  in  Cali- 
fornia. II.  Feeding  Trials  with 
Cereal  Hays. 

Bark  Diseases  of  Citrus  Trees  in  Cali- 
fornia. 

The  Mat  Bean,  Phaseolus  Aconitifo- 
lius. 

Manuf acture  of  Roquefort  Type  Cheese 
from  Goat's  Milk. 

Orchard   Heating  in   California. 

The  Utilization  of  Surplus  Plums. 

The  Codling  Moth  in  Walnuts. 

The  Dehydration  of  Prunes. 

Citrus   Culture   in   Central   California. 

Stationary  Spray  Plants  in  California. 

Yield,  Stand,  and  Volume  Tables  for 
White  Fir  in  the  California  Pine 
Region. 

Alternaria  Rot  of  Lemons. 

The  Digestibility  of  Certain  Fruit  By- 
products as  Determined  for  Rumi- 
nants. Part  I.  Dried  Orange  Pulp 
and  Raisin  Pulp. 

Factors  Influencing  the  Quality  of 
Fresh  Asparagus  after  it  is  Har- 
vested. 

Paradichlorobenzene  as  a  Soil  Fumi- 
gant. 

A  Study  of  the  Relative  Value  of  Cer- 
tain Root  Crops  and  Salmon  Oil  as 
Sources   of   Vitamin   A  for   Poultry. 

Planting  and  Thinning  Distances  for 
Deciduous  Fruit  Trees. 

The  Tractor  on  California  Farms. 

Culture  of  the  Oriental  Persimmon  in 
California. 

Poultry  Feeding  :  Principles  and  Prac- 
tice. 

A  Study  of  Various  Rations  for  Fin- 
ishing Range  Calves    as  Baby  Beeves. 

Economic  Aspects  of  the  Cantaloupe 
Industry. 

Rice  and  Rice  By-Products  as  Feeds 
for  Fattening  Swine. 

Beef   Cattle  Feeding   Trials,    1921-24. 

Cost  of  Producing  Almonds  in  Cali- 
fornia :  a  Progress  Report. 

Apricots  (Series  on  California  Crops 
and  Prices). 

The  Relation  of  Rate  of  Maturity  to 
Egg  Production. 

Apple  Growing  in  California. 

Apple  Pollination  Studies  in  Cali- 
fornia. 

The  Value  of  Orange  Pulp  for  Milk 
Production. 

The  Relation  of  Maturity  of  Cali- 
fornia Plums  to  Shipping  and 
Dessert  Quality. 

Economic  Status  of  the  Grape  Industry. 

Range  Grasses  of  California. 

Raisin  By-Products  and  Bean  Screen- 
ings as  Feeds  for  Fattening  Lambs. 

Some  Economic  Problems  Involved  in 
the  Pooling  of  Fruit. 

PoAver  Requirements  of  Electrically 
Driven    Manufacturing    Equipment. 


bulletins- 
no. 

434.  Investigations  on  the  Use  of  Fruits  in 

Ice  Cream  and  Ices. 

435.  The      Problem      of      Securing      Closer 

Relationship  Between  Agricultural 
Development  and  Irrigation  Con- 
struction. 

436.  I.   The   Kadota   Fig.      II.   Kadota   Fig 

Products. 

437.  Economic    Aspects    of    the    Dairy    In- 

dustry. 

438.  Grafting  Affinities  with  Special  Refer- 

ence to  Plums. 

439.  The  Digestibility  of  Certain  Fruit  By- 

products as  Determined  for  Rumi- 
nants. Part  II.  Dried  Pineapple 
Pulp,  Dried  Lemon  Pulp,  and  Dried 
Olive  Pulp. 

CIRCULARS 

No.  No. 

87.   Alfalfa.  257. 
115.   Grafting   Vinifera   Vineyards. 

117.   The    selection    and    Cost    of    a    Small  258. 

Pumping   Plant.  259. 

127.   House  Fumigation.  261. 

129.   The  control  of  Citrus  Insects.  264. 
136.  Melilotus    Indica    as    a    Green-Manure 

Crop  for  California.  265. 

144.   Oidium    or    Powdery    Mildew    of    the  266. 

Vine. 

157.   Control  of  Pear   Scab.  267. 
164.   Small   Fruit   Culture   in   California. 

166.  The  County  Farm  Bureau.  269. 

173.   The    Construction    of   the    Wood-Hoop  270. 

Silo.  273. 

178.  The  Packing  of  Apples  in  California.  276. 

179.  Factors   of    Importance   in    Producing  277. 

Milk  of  Low  Bacterial  Count. 

202.  County    Organization    for    Rural    Fire  278. 

Control. 

203.  Peat   as   a   Manure   Substitute.  279. 
209.   The  Function  of  the  Farm  Bureau. 

212.   Salvaging  Rain-Damaged  Prunes.  281. 

215.  Feeding  Dairy   Cows  in   California. 
217.  Methods   for*  Marketing  Vegetables   in 

California.  282. 

230.  Testing  Milk,    Cream,    and   Skim  Milk 

for  Butterfat.  283. 

231.  The  Home  Vineyard.  284. 

232.  Harvesting    and    Handling    California  286. 

Cherries   for   Eastern    Shipment.  287. 

234.  Winter     Injury     to     Young     Walnut  288. 

Trees  During  1921-1922.  289. 

238.  The   Apricot  in   California.  290. 

239.  Harvesting     and     Handling     Apricots  292. 

and  Plums  for  Eastern  Shipment.  293. 

240.  Harvesting    and    Handling    California  294. 

Pears  for  Eastern  Shipment.  296. 

241.  Harvesting    and    Handling    California 

Peaches  for  Eastern   Shipment.  298. 

243.  Marmalade     Juice     and     Jelly     Juice 

from   Citrus  Fruits.  300. 

244.  Central  Wire  Bracing  for  Fruit  Trees.  301. 

245.  Vine  Pruning   Systems.  302. 

248.  Some   Common  Errors  in  Vine  Prun-  304. 

ing  and  Their  Remedies.  305. 

249.  Replacing  Missing  Vines.  306. 

250.  Measurement   of   Irrigation   Water   on 

the  Farm.  307. 

252.  Support   for   Vines.  308. 

253.  Vineyard   Plans.  309. 

254.  The    Use    of    Artificial  Light    to    In-               310. 

crease  Winter  Egg  Production. 

255.  Leguminous    Plants    as    Organic    Fer-  311. 

tilizers  in   California   Agriculture. 


(Continued) 
No. 

440.  The  Feeding  Value  of  Raisins  and 
Dairy  By-Products  for  Growing  and 
Fattening  Swine. 

441.  The  Electric  Brooder. 

442.  Laboratory  Tests  of  Orchard  Heaters. 

443.  Standardization  and  Improvement  of 
California   Butter. 

444.  Series  on  California  Crops  and  Prices  : 
Beans. 

445.  Economic  Aspects  of  the  Apple  In- 
dustry. 


The  Small-Seeded  Horse  Bean  (Vicia 
faba   var.   minor). 

Thinning   Deciduous   Fruits. 

Pear  By-Products. 

Sewing  Grain  Sacks. 

Preliminary  Essentials  to  Bovine  Tu- 
berculosis Control  in   California. 

Plant   Disease  and   Pest   Control. 

Analyzing  the  Citrus  Orchard  by 
Means  of  Simple  Tree  Records. 

The  Tendency  of  Tractors  to  Rise  in 
Front;  Causes  and  Remedies. 

An   Orchard   Brush  Burner. 

A  Farm  Septic  Tank. 

Saving  the  Gophered   Citrus  Tree. 

Home   Canning. 

Head,  Cane  and  Cordon  Pruning  of 
Vines. 

Olive  Pickling  in  Mediterranean 
Countries. 

The  Preparation  and  Refining  of 
Olive  Oil  in  Southern  Europe. 

The  Results  of  a  Survey  to  Deter- 
mine the  Cost  of  Producing  Beef  in 
California. 

Prevention  of  Insect  Attack  on  Stored 
Grain. 

Fertilizing  Citrus  Trees  in  California. 

The  Almond  in   California. 

Milk  Houses  for  California  Dairies. 

Potato   Production  in   California. 

Phylloxera  Resistant  Vineyards. 

Oak  Fungus  in   Orchard  Trees. 

The  Tangier  Pea. 

Alkali   Soils. 

The    Basis   of   Grape    Standardization. 

Propagation   of   Deciduous  Fruits. 

Control  of  the  California  Ground 
Squirrel. 

Possibilities  and  Limitations  of  Coop- 
erative Marketing. 

Coccidiosis  of  Chickens. 

Buckeye  Poisoning  of  the  Honey  Bee. 

The   Sugar  Beet  in  California. 

Drainage  on  the  Farm. 

Liming  the   Soil. 

A  General  Purpose  Soil  Auger  and 
Its  Use  on  the  Farm. 

American   Foulbrood   and   Its  Control. 

Cantaloupe   Production   in    California. 

Fruit  Tree  and   Orchard  Judging. 

The  Operation  of  the  Bacteriological 
Laboratory  for  Dairy  Plants. 

The  Improvement  of   Quality  in  Figs. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


2lw  L'28 


